Privoxy Frequently Asked Questions
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4. Miscellaneous

4.1. How much does Privoxy slow my browsing down? This -has to add extra time to browsing.

How much of an impact depends on many things, including the CPU of the host - system, how aggressive the configuration is, which specific actions are being triggered, - the size of the page, the bandwidth of the connection, etc.

Overall, it should not slow you down any in real terms, and may actually help - speed things up since ads, banners and other junk are not typically being - retrieved and displayed. The actual processing time required by - Privoxy itself for each page, is relatively small - in the overall scheme of things, and happens very quickly. This is typically - more than offset by time saved not downloading and rendering ad images (if ad - blocking is being used).

"Filtering" content via the filter or - deanimate-gifs - actions will certainly cause a perceived slowdown, since the entire document - needs to be buffered before displaying. And on very large documents, filtering may have - some measurable impact. How much depends on the page size, the actual - definition of the filter(s), etc. See below. Most other actions have little - to no impact on speed.

- Also, when filtering is enabled, typically there is a disabling of - compression, (see prevent-compression). - This can have an impact on speed as well. Again, the page size, etc. will - determine how much of an impact.

4.2. I notice considerable -delays in page requests compared to the old Junkbuster. What's wrong?

If you use any filter action, - such as filtering banners by size, web-bugs etc, or the deanimate-gifs - action, the entire document must be loaded into memory in order for the filtering - mechanism to work, and nothing is sent to the browser during this time.

The loading time typically does not really change much in real numbers, but - the feeling is different, because most browsers are able to start rendering - incomplete content, giving the user a feeling of "it works". This effect is - more noticeable on slower dialup connections. Extremely large documents - may have some impact on the time to load the page where there is filtering - being done. But overall, the difference should be very minimal. If there is a - big impact, then probably some other situation is contributing (like - anti-virus software). -

Filtering is automatically disabled for inappropriate MIME types. But note - that if the web server mis-reports the MIME type, then content that should - not be filtered, could be. Privoxy only knows how - to differentiate filterable content because of the MIME type as reported by - the server, or because of some configuration setting that enables/disables - filtering.

4.3. What are "http://config.privoxy.org/" and -"http://p.p/"?

http://config.privoxy.org/ is the - address of Privoxy's built-in user interface, and - http://p.p/ is a shortcut for it.

Since Privoxy sits between your web browser and the Internet, - it can simply intercept requests for these addresses and answer them with its built-in - "web server".

This also makes for a good test for your browser configuration: If entering the - URL http://config.privoxy.org/ - takes you to a page saying "This is Privoxy ...", everything is OK. - If you get a page saying "Privoxy is not working" instead, then - your browser didn't use Privoxy for the request, - hence it could not be intercepted, and you have accessed the real - web site at config.privoxy.org.

With recent versions of Privoxy (version 2.9.x and - later), the user interface features information on the run time status, the - configuration, and even a built-in editor for the actions files.

Note that the built-in URLs from earlier versions of Junkbuster - / Privoxy, http://example.com/show-proxy-args and http://i.j.b/, - are no longer supported. If you still use such an old version, you should really consider - upgrading to 3.0.6.

4.4. How can I submit new ads, or report -problems?

Please see the Contact section for -various ways to interact with the developers.

4.5. If I do submit missed ads, will -they be included in future updates?

Whether such submissions are eventually included in the - default.action configuration file depends on how - significant the issue is. We of course want to address any potential - problem with major, high-profile sites such as Google, - Yahoo, etc. Any site with global or regional reach, - has a good chance of being a candidate. But at the other end of the spectrum - are any number of smaller, low-profile sites such as for local clubs or - schools. Since their reach and impact are much less, they are best handled by - inclusion in the user's user.action, and thus would be - unlikely to be included.

4.6. Why doesn't anyone answer my support -request?

Rest assured that it has been read and considered. Why it is not answered, -could be for various reasons, including no one has a good answer for it, no -one has had time to yet investigate it thoroughly, it has been reported -numerous times already, or because not enough information was provided to help -us help you. Your efforts are not wasted, and we do appreciate them.

4.7. How can I hide my IP address?

If you run both the browser and Privoxy locally, you cannot hide your IP - address with Privoxy or ultimately any other - software alone. The server needs to know your IP address so that it knows - where to send the responses back.

There are many publicly usable "anonymous" proxies out there, which - provide a further level of indirection between you and the web server.

However, these proxies are called "anonymous" because you don't need - a password, not because they would offer any real anonymity. - Most of them will log your IP address and make it available to the - authorities in case you violate the law of the country they run in. In fact - you can't even rule out that some of them only exist to *collect* information - on (those suspicious) people with a more than average preference for privacy.

Your best bet is to chain Privoxy - with Tor, - an EFF supported onion routing system. - The configuration details can be found in - How do I use Privoxy together with Tor section - just below.

4.8. Can Privoxy guarantee I am anonymous?

No. Your chances of remaining anonymous are greatly improved, but unless you - chain Privoxy with Tor - or a similar system and know what you're doing when it comes to configuring - the rest of your system, it would be safest to assume that everything you do - on the Web can be traced back to you.

Privoxy can remove various information about you, - and allows you more freedom to decide which sites - you can trust, and what details you want to reveal. But it neither - hides your IP address, nor can it guarantee that the rest of the system - behaves correctly. There are several possibilities how a web sites can find - out who you are, even if you are using a strict Privoxy - configuration and chained it with Tor.

Most of Privoxy's protection can be easily subverted - by an insecure browser configuration, therefore you should use a browser that can - be configured to only execute code from trusted sites, and be careful which sites you trust. - For example there is no point in having Privoxy - modify the User-Agent header, if websites can get all the information they want - through JavaScript, ActiveX, Flash, Java etc.

A few browsers disclose the user's email address in certain situations, such - as when transferring a file by FTP. Privoxy - does not filter FTP. If you need this feature, or are concerned about the - mail handler of your browser disclosing your email address, you might - consider products such as NSClean.

Browsers available only as binaries could use non-standard headers to give - out any information they can have access to: see the manufacturer's license - agreement. It's impossible to anticipate and prevent every breach of privacy - that might occur. The professionally paranoid prefer browsers available as - source code, because anticipating their behavior is easier. Trust the source, - Luke!

4.9. A test site says I am not using a Proxy.

Good! Actually, they are probably testing for some other kinds of proxies. - Hiding yourself completely would require additional steps.

4.10. How do I use Privoxy - together with Tor?

Before you configure Privoxy to use Tor - (http://tor.eff.org/), - please follow the User Manual chapters - 2. Installation and - 5. Startup to make sure - Privoxy itself is setup correctly.

- If it is, refer to Tor's - extensive documentation to learn how to install Tor, - and make sure Tor's logfile says that - "Tor has successfully opened a circuit" and it - "looks like client functionality is working".

If either Tor or Privoxy - isn't working, their combination most likely will neither. Testing them on their - own will also help you to direct problem reports to the right audience. - If Privoxy isn't working, don't bother the - Tor developers. If Tor - isn't working, don't send bug reports to the Privoxy Team.

If you verified that Privoxy and Tor - are working, it is time to connect them. As far as Privoxy - is concerned, Tor is just another proxy that can be reached - by socks4 or socks4a. Most likely you are interested in Tor - to increase your anonymity level, therefore you should use socks4a, - to make sure Privoxy's DNS requests are - done through Tor and thus invisible to your local network.

Since Privoxy 3.0.5, its - main configuration file - is already prepared for Tor, if you are using a - default Tor configuration and run it on the same - system as Privoxy, you just have to edit the - forwarding section - and uncomment the line:

# forward-socks4a / 127.0.0.1:9050 . -

This is enough to reach the Internet, but additionally you should - uncomment the following forward rules, to make sure your local network is still - reachable through Privoxy:

+ +
# forward 192.168.*.*/ . + + + + + Miscellaneous + + + + + + + + + +
+ + + + + + + + + +
+ Privoxy Frequently Asked Questions +
+ Prev + + + Next +
+
+
+
+
+ 4. Miscellaneous +
+
+
+ 4.1. How much does Privoxy slow my browsing down? + This has to add extra time to browsing. +
+
+ How much of an impact depends on many things, including the CPU of + the host system, how aggressive the configuration is, which + specific actions are being triggered, the size of the page, the + bandwidth of the connection, etc. +
+
+ Overall, it should not slow you down any in real terms, and may + actually help speed things up since ads, banners and other junk are + not typically being retrieved and displayed. The actual processing + time required by Privoxy itself + for each page, is relatively small in the overall scheme of things, + and happens very quickly. This is typically more than offset by + time saved not downloading and rendering ad images and other junk + content (if ad blocking is being used). +
+
+ "Filtering" content via the filter or deanimate-gifs actions may cause a perceived + slowdown, since the entire document needs to be buffered before + displaying. And on very large documents, filtering may have some + measurable impact. How much depends on the page size, the actual + definition of the filter(s), etc. See below. Most other actions + have little to no impact on speed. +
+
+ Also, when filtering is enabled but zlib support isn't available, + compression is often disabled (see prevent-compression). This can have an impact on speed + as well, although it's probably smaller than you might think. + Again, the page size, etc. will determine how much of an impact. +
+
+
+
+ 4.2. I notice considerable delays in page + requests. What's wrong? +
+
+ If you use any filter action, such as filtering banners by size, + web-bugs etc, or the deanimate-gifs action, the entire document must be + loaded into memory in order for the filtering mechanism to work, + and nothing is sent to the browser during this time. +
+
+ The loading time typically does not really change much in real + numbers, but the feeling is different, because most browsers are + able to start rendering incomplete content, giving the user a + feeling of "it works". This effect is more noticeable on slower + dialup connections. Extremely large documents may have some impact + on the time to load the page where there is filtering being done. + But overall, the difference should be very minimal. If there is a + big impact, then probably some other situation is contributing + (like anti-virus software). +
+
+ Filtering is automatically disabled for inappropriate MIME types. + But note that if the web server mis-reports the MIME type, then + content that should not be filtered, could be. Privoxy only knows how to differentiate + filterable content because of the MIME type as reported by the + server, or because of some configuration setting that + enables/disables filtering. +
+
+
+
+ 4.3. What are "http://config.privoxy.org/" and + "http://p.p/"? +
+
+ http://config.privoxy.org/ is the address of Privoxy's built-in user interface, and + http://p.p/ is a shortcut + for it. +
+
+ Since Privoxy sits between your + web browser and the Internet, it can simply intercept requests for + these addresses and answer them with its built-in "web server". +
+
+ This also makes for a good test for your browser configuration: If + entering the URL http://config.privoxy.org/ takes you to a page saying + "This is Privoxy ...", everything is OK. + If you get a page saying "Privoxy is not + working" instead, then your browser didn't use Privoxy for the request, hence it could not be + intercepted, and you have accessed the real web site at config.privoxy.org. +
+
+ Note that config.privoxy.org resolves to a public IP address. If + you use config.privoxy.org as ping or traceroute target you will + reach the system on the Internet (Privoxy can't intercept ICMP + requests). If you want to ping the system Privoxy runs on, you + should use its IP address or local DNS name (if it has got one). +
+
+
+
+ 4.4. How can I submit new ads, or report + problems? +
+
+ Please see the Contact section for + various ways to interact with the developers. +
+
+
+
+ 4.5. If I do submit missed ads, will they be + included in future updates? +
+
+ Whether such submissions are eventually included in the default.action configuration file depends on how + significant the issue is. We of course want to address any + potential problem with major, high-profile sites such as Google, Yahoo, etc. Any + site with global or regional reach, has a good chance of being a + candidate. But at the other end of the spectrum are any number of + smaller, low-profile sites such as for local clubs or schools. + Since their reach and impact are much less, they are best handled + by inclusion in the user's user.action, + and thus would be unlikely to be included. +
+
+
+
+ 4.6. Why doesn't anyone answer my support + request? +
+
+ Rest assured that it has been read and considered. Why it is not + answered, could be for various reasons, including no one has a good + answer for it, no one has had time to yet investigate it + thoroughly, it has been reported numerous times already, or because + not enough information was provided to help us help you. Your + efforts are not wasted, and we do appreciate them. +
+
+
+
+ 4.7. How can I hide my IP address? +
+
+ If you run both the browser and Privoxy locally, you cannot hide your IP + address with Privoxy or ultimately + any other software alone. The server needs to know your IP address + so that it knows where to send the responses back. +
+
+ There are many publicly usable "anonymous" proxies out there, which + provide a further level of indirection between you and the web + server. +
+
+ However, these proxies are called "anonymous" because you don't + need to authenticate, not because they would offer any real + anonymity. Most of them will log your IP address and make it + available to the authorities in case you violate the law of the + country they run in. In fact you can't even rule out that some of + them only exist to *collect* information on (those suspicious) + people with a more than average preference for privacy. +
+
+ If you want to hide your IP address from most adversaries, you + should consider chaining Privoxy + with Tor. + The configuration details can be found in How do I use Privoxy + together with Tor section just + below. +
+
+
+
+ 4.8. Can Privoxy guarantee I am + anonymous? +
+
+ No. Your chances of remaining anonymous are improved, but unless + you chain Privoxy with Tor or a similar proxy and know what + you're doing when it comes to configuring the rest of your system, + you should assume that everything you do on the Web can be traced + back to you. +
+
+ Privoxy can remove various + information about you, and allows you more freedom to decide which sites you + can trust, and what details you want to reveal. But it neither + hides your IP address, nor can it guarantee that the rest of the + system behaves correctly. There are several possibilities how a web + sites can find out who you are, even if you are using a strict + Privoxy configuration and chained + it with Tor. +
+
+ Most of Privoxy's + privacy-enhancing features can be easily subverted by an insecure + browser configuration, therefore you should use a browser that can + be configured to only execute code from trusted sites, and be + careful which sites you trust. For example there is no point in + having Privoxy modify the + User-Agent header, if websites can get all the information they + want through JavaScript, ActiveX, Flash, Java etc. +
+
+ A few browsers disclose the user's email address in certain + situations, such as when transferring a file by FTP. Privoxy does not filter FTP. If you need this + feature, or are concerned about the mail handler of your browser + disclosing your email address, you might consider products such as + NSClean. +
+
+ Browsers available only as binaries could use non-standard headers + to give out any information they can have access to: see the + manufacturer's license agreement. It's impossible to anticipate and + prevent every breach of privacy that might occur. The + professionally paranoid prefer browsers available as source code, + because anticipating their behavior is easier. Trust the source, + Luke! +
+
+
+
+ 4.9. A test site says I am not using a + Proxy. +
+
+ Good! Actually, they are probably testing for some other kinds of + proxies. Hiding yourself completely would require additional steps. +
+
+
+
+ 4.10. How do I use Privoxy together with Tor? +
+
+ Before you configure Privoxy to + use Tor, + please follow the User Manual chapters 2. + Installation and 5. Startup to make sure Privoxy itself is setup correctly. +
+
+ If it is, refer to Tor's + extensive documentation to learn how to install Tor, and make sure Tor's logfile says that "Tor has successfully opened a circuit" and it "looks like client functionality is working". +
+
+ If either Tor or Privoxy isn't working, their combination most + likely will neither. Testing them on their own will also help you + to direct problem reports to the right audience. If Privoxy isn't working, don't bother the Tor developers. If Tor isn't working, don't send bug reports to + the Privoxy Team. +
+
+ If you verified that Privoxy and + Tor are working, it is time to + connect them. As far as Privoxy is + concerned, Tor is just another + proxy that can be reached by socks4, socks4a and socks5. Most + likely you are interested in Tor + to increase your anonymity level, therefore you should use socks5, + to make sure DNS requests are done through Tor and thus invisible to your local network. + Using socks4a would work too, but with socks5 you get more precise + error messages. +
+
+ Privoxy's main configuration + file is already prepared for Tor, if you are using a default Tor configuration and run it on the same + system as Privoxy, you just have + to edit the forwarding section and uncomment the line: +
+
+
+ + + + +
+
+# forward-socks5t / 127.0.0.1:9050 . +
+
+ +
+ Note that if you got Tor through one of the bundles, you may have + to change the port from 9050 to 9150 (or even another one). For + details, please check the documentation on the Tor website. +
+
+ This is enough to reach the Internet, but additionally you might + want to uncomment the following forward rules, to make sure your + local network is still reachable through Privoxy: +
+
+
+ + +
+
+# forward 192.168.*.*/ . # forward 10.*.*.*/ . # forward 127.*.*.*/ . -
Unencrypted connections to systems in these address ranges will - be as (un)secure as the local network is, but the alternative is - that you can't reach the network at all. - If you also want to be able to reach servers in your local - network by using their names, you will need additional - exceptions that look like this:

# forward localhost/ . -
Save the modified configuration file and open - http://config.privoxy.org/show-status/ - in your browser, confirm that Privoxy has reloaded its configuration - and that there are no other forward lines, unless you know that you need them. If everything looks good, - refer to - Tor - Faq 4.2 to learn how to verify that you are really using Tor.
Afterward, please take the time to at least skim through the rest - of Tor's documentation. Make sure you understand - what Tor does, why it is no replacement for - application level security, and why you shouldn't use it for unencrypted logins.
4.11. Might some things break because header information or -content is being altered?
Definitely. It is common for sites to use browser type, browser version, - HTTP header content, and various other techniques in order to dynamically - decide what to display and how to display it. What you see, and what I see, - might be very different. There are many, many ways that this can be handled, - so having hard and fast rules, is tricky.
"User-Agent" is often used in this way to identify - the browser, and adjust content accordingly. Changing this now (at least not - further than removing the OS information) is not recommended, since so many - sites do look for it. You may get undesirable results by changing just this - one aspect.
Also, different browsers use different encodings of Russian and Czech - characters, certain web servers convert pages on-the-fly according to the - User Agent header. Giving a "User Agent" with the wrong - operating system or browser manufacturer causes some sites in these languages - to be garbled; Surfers to Eastern European sites should change it to - something closer. And then some page access counters work by looking at the - "Referer" header; they may fail or break if unavailable. The - weather maps of Intellicast have been blocked by their server when no - "Referer" or cookie is provided, is another example. (But you - can forge both headers without giving information away). There are - many other ways things that can go wrong when trying to fool a web server. The - results of which could inadvertently cause pages to load incorrectly, - partially, or even not at all. And there may be no obvious clues as to just - what went wrong, or why. Nowhere will there be a message that says - "Turn off fast-redirects or else! - "
Similar thoughts apply to modifying JavaScript, and, to a lesser degree, - HTML elements.
If you have problems with a site, you will have to adjust your configuration - accordingly. Cookies are probably the most likely adjustment that may - be required, but by no means the only one.
4.12. Can Privoxy act as a "caching" proxy to -speed up web browsing?
No, it does not have this ability at all. You want something like - Squid for this. And, yes, - before you ask, Privoxy can co-exist - with other kinds of proxies like Squid. - See the forwarding - chapter in the user - manual for details.
4.13. What about as a firewall? Can Privoxy protect me?
Not in the way you mean, or in the way a true firewall can. - Privoxy can help protect your privacy, but not - protect you from intrusion attempts. It is, of course, perfectly possible - and recommended to use both.
4.14. I have large empty spaces / a checkerboard pattern now where -ads used to be. Why?
It is technically possible to eliminate banners and ads in a way that frees - their allocated page space. This could easily be done by blocking with - Privoxy's filters, - and eliminating the entire image references from the - HTML page source.
But, this would consume considerably more CPU resources (IOW, slow things - down), would likely destroy the layout of some web pages which rely on the - banners utilizing a certain amount of page space, and might fail in other - cases, where the screen space is reserved (e.g. by HTML tables for instance). - Also, making ads and banners disappear without any trace complicates - troubleshooting, and would sooner or later be problematic.
The better alternative is to instead let them stay, and block the resulting - requests for the banners themselves as is now the case. This leaves either - empty space, or the familiar checkerboard pattern.
So the developers won't support this in the default configuration, but you - can of course define appropriate filters yourself to achieve this.
4.15. How can Privoxy filter Secure (HTTPS) URLs?
Since secure HTTP connections are encrypted SSL sessions between your browser - and the secure site, and are meant to be reliably secure, - there is little that Privoxy can do but hand the raw - gibberish data though from one end to the other unprocessed.
The only exception to this is blocking by host patterns, as the client needs - to tell Privoxy the name of the remote server, - so that Privoxy can establish the connection. - If that name matches a host-only pattern, the connection will be blocked.
As far as ad blocking is concerned, this is less of a restriction than it may - seem, since ad sources are often identifiable by the host name, and often - the banners to be placed in an encrypted page come unencrypted nonetheless - for efficiency reasons, which exposes them to the full power of - Privoxy's ad blocking.
"Content cookies" (those that are embedded in the actual HTML or - JS page content, see filter{content-cookies}), - in an SSL transaction will be impossible to block under these conditions. - Fortunately, this does not seem to be a very common scenario since most - cookies come by traditional means.
4.16. Privoxy runs as a "server". How -secure is it? Do I need to take any special precautions?
There are no known exploits that might affect - Privoxy. On Unix-like systems, - Privoxy can run as a non-privileged - user, which is how we recommend it be run. Also, by default - Privoxy only listens to requests - from "localhost" only. The server aspect of - Privoxy is not itself directly exposed to the - Internet in this configuration. If you want to have - Privoxy serve as a LAN proxy, this will have to - be opened up to allow for LAN requests. In this case, we'd recommend - you specify only the LAN gateway address, e.g. 192.168.1.1, in the main - Privoxy configuration file and check all access control and security - options. All LAN hosts can then use this as their proxy address - in the browser proxy configuration, but Privoxy - will not listen on any external interfaces. ACLs can be defined in addition, - and using a firewall is always good too. Better safe than sorry.
4.17. How can I temporarily disable Privoxy?
The easiest way is to access Privoxy with your - browser by using the remote toggle URL: http://config.privoxy.org/toggle. - See the Bookmarklets section - of the User Manual for an easy way to access this - feature.
4.18. When "disabled" is Privoxy totally -out of the picture?
No, this just means all filtering and actions are disabled. - Privoxy is still acting as a proxy, but just not - doing any of the things that Privoxy would - normally be expected to do. It is still a "middle-man" in - the interaction between your browser and web sites. See below to bypass - the proxy.
4.19. How can I tell Privoxy to totally ignore certain sites?
Bypassing a proxy, or proxying based on arbitrary criteria, is purely a browser - configuration issue, not a Privoxy issue. Modern browsers typically do have - settings for not proxying certain sites. Check your browser's help files.
4.20. My logs show Privoxy "crunches" -ads, but also its own internal CGI pages. What is a "crunch"?
A "crunch" simply means Privoxy intercepted - something, nothing more. Often this is indeed ads or - banners, but Privoxy uses the same mechanism for - trapping requests for its own internal pages. For instance, a request for - Privoxy's configuration page at: http://config.privoxy.org, is - intercepted (i.e. it does not go out to the 'net), and the familiar CGI - configuration is returned to the browser, and the log consequently will show - a "crunch".
4.21. Can Privoxy effect files that I download -from a webserver? FTP server?
From the webserver's perspective, there is no difference between - viewing a document (i.e. a page), and downloading a file. The same is true of - Privoxy. If there is a match for a block pattern, - it will still be blocked, and of course this is obvious. -
Filtering is potentially more of a concern since the results are not always - so obvious, and the effects of filtering are there whether the file is simply - viewed, or downloaded. And potentially whether the content is some obnoxious - advertisement, or Mr. Jimmy's latest/greatest source code jewel. Of course, - one of these presumably is "bad" content that we don't want, and - the other is "good" content that we do want. - Privoxy is blind to the differences, and can only - distinguish "good from bad" by the configuration parameters - we give it.
Privoxy knows the differences in files according - to the "Document Type" as reported by the webserver. If this is - reported accurately (e.g. "application/zip" for a zip archive), - then Privoxy knows to ignore these where - appropriate. Privoxy potentially can filter HTML - as well as plain text documents, subject to configuration parameters of - course. Also, documents that are of an unknown type (generally assumed to be - "text/plain") can be filtered, as will those that might be - incorrectly reported by the webserver. If such a file is a downloaded file - that is intended to be saved to disk, then any content that might have been - altered by filtering, will be saved too, for these (probably rare) cases.
Note that versions later than 3.0.2 do NOT filter document types reported as - "text/plain". Prior to this, Privoxy - did filter this document type.
In short, filtering is "ON" if a) the Document Type as reported - by the webserver is appropriate and b) the configuration - allows it (or at least does not disallow it). That's it. There is no magic - cookie anywhere to say this is "good" and this is - "bad". It's the configuration that let's it all happen or not.
If you download text files, you probably do not want these to be filtered, - particularly if the content is source code, or other critical content. Source - code sometimes might be mistaken for Javascript (i.e. the kind that might - open a pop-up window). It is recommended to turn off filtering for download - sites (particularly if the content may be plain text files and you are using - version 3.0.2 or earlier) in your user.action file. And - also, for any site or page where making any changes at - all to the content is to be avoided.
Privoxy does not do FTP at all, only HTTP - and HTTPS (SSL) protocols, so please don't try.
4.22. I just downloaded a Perl script, and Privoxy -altered it! Yikes, what is wrong!
Please read above.
4.23. Should I continue to use a "HOSTS" file for ad-blocking?
One time-tested technique to defeat common ads is to trick the local DNS - system by giving a phony IP address for the ad generator in the local - HOSTS file, typically using 127.0.0.1, aka - localhost. This effectively blocks the ad.
There is no reason to use this technique in conjunction with - Privoxy. Privoxy - does essentially the same thing, much more elegantly and with much more - flexibility. A large HOSTS file, in fact, not only - duplicates effort, but may get in the way. It is recommended to remove - such entries from your HOSTS file. If you think - your hosts list is neglected by Privoxy's - configuration, consider adding your list to your user.action file:
+ +
{ +block } +
+
+ +
+ Unencrypted connections to systems in these address ranges will be + as (un)secure as the local network is, but the alternative is that + your browser can't reach the network at all. Then again, that may + actually be desired and if you don't know for sure that your + browser has to be able to reach the local network, there's no + reason to allow it. +
+
+ If you want your browser to be able to reach servers in your local + network by using their names, you will need additional exceptions + that look like this: +
+
+
+ + + + +
+
+# forward localhost/ . +
+
+ +
+ Save the modified configuration file and open http://config.privoxy.org/show-status in your browser, + confirm that Privoxy has reloaded + its configuration and that there are no other forward lines, unless + you know that you need them. If everything looks good, refer to Tor Faq 4.2 to learn how to verify that you are + really using Tor. +
+
+ Afterward, please take the time to at least skim through the rest + of Tor's documentation. Make sure + you understand what Tor does, why + it is no replacement for application level security, and why you + probably don't want to use it for unencrypted logins. +
+
+
+
+ 4.11. Might some things break because header + information or content is being altered? +
+
+ Definitely. It is common for sites to use browser type, browser + version, HTTP header content, and various other techniques in order + to dynamically decide what to display and how to display it. What + you see, and what I see, might be very different. There are many, + many ways that this can be handled, so having hard and fast rules, + is tricky. +
+
+ The "User-Agent" is sometimes used in + this way to identify the browser, and adjust content accordingly. +
+
+ Also, different browsers use different encodings of non-English + characters, certain web servers convert pages on-the-fly according + to the User Agent header. Giving a "User + Agent" with the wrong operating system or browser + manufacturer causes some sites in these languages to be garbled; + Surfers to Eastern European sites should change it to something + closer. And then some page access counters work by looking at the + "Referer" header; they may fail or break + if unavailable. The weather maps of Intellicast have been blocked + by their server when no "Referer" or + cookie is provided, is another example. (But you can forge both + headers without giving information away). There are many other ways + things can go wrong when trying to fool a web server. The results + of which could inadvertently cause pages to load incorrectly, + partially, or even not at all. And there may be no obvious clues as + to just what went wrong, or why. Nowhere will there be a message + that says "Turn off fast-redirects or + else! " +
+
+ Similar thoughts apply to modifying JavaScript, and, to a lesser + degree, HTML elements. +
+
+ If you have problems with a site, you will have to adjust your + configuration accordingly. Cookies are probably the most likely + adjustment that may be required, but by no means the only one. +
+
+
+
+ 4.12. Can Privoxy act as a "caching" proxy to speed up web browsing? +
+
+ No, it does not have this ability at all. You want something like + Squid or Polipo for this. And, yes, before you ask, Privoxy can co-exist with other kinds of + proxies like Squid. See the forwarding chapter in the user manual for + details. +
+
+
+
+ 4.13. What about as a firewall? Can Privoxy + protect me? +
+
+ Not in the way you mean, or in the way some firewall vendors claim + they can. Privoxy can help protect + your privacy, but can't protect your system from intrusion + attempts. It is, of course, perfectly possible to use both. +
+
+
+
+ 4.14. I have large empty spaces / a checkerboard + pattern now where ads used to be. Why? +
+
+ It is technically possible to eliminate banners and ads in a way + that frees their allocated page space. This could easily be done by + blocking with Privoxy's filters, + and eliminating the entire image references from the HTML page + source. +
+
+ But, this would consume considerably more CPU resources (IOW, slow + things down), would likely destroy the layout of some web pages + which rely on the banners utilizing a certain amount of page space, + and might fail in other cases, where the screen space is reserved + (e.g. by HTML tables for instance). Also, making ads and banners + disappear without any trace complicates troubleshooting, and would + sooner or later be problematic. +
+
+ The better alternative is to instead let them stay, and block the + resulting requests for the banners themselves as is now the case. + This leaves either empty space, or the familiar checkerboard + pattern. +
+
+ So the developers won't support this in the default configuration, + but you can of course define appropriate filters yourself to + achieve this. +
+
+
+
+ 4.15. How can Privoxy filter Secure (HTTPS) URLs? +
+
+ Since secure HTTP connections are encrypted SSL sessions between + your browser and the secure site, and are meant to be reliably + secure, there + is little that Privoxy can do but + hand the raw gibberish data though from one end to the other + unprocessed. +
+
+ The only exception to this is blocking by host patterns, as the + client needs to tell Privoxy the + name of the remote server, so that Privoxy can establish the connection. If that + name matches a host-only pattern, the connection will be blocked. +
+
+ As far as ad blocking is concerned, this is less of a restriction + than it may seem, since ad sources are often identifiable by the + host name, and often the banners to be placed in an encrypted page + come unencrypted nonetheless for efficiency reasons, which exposes + them to the full power of Privoxy's ad blocking. +
+
+ "Content cookies" (those that are + embedded in the actual HTML or JS page content, see filter{content-cookies}), in an SSL transaction + will be impossible to block under these conditions. Fortunately, + this does not seem to be a very common scenario since most cookies + come by traditional means. +
+
+
+
+ 4.16. Privoxy runs as a "server". How secure is it? Do I need to take any + special precautions? +
+
+ On Unix-like systems, Privoxy can + run as a non-privileged user, which is how we recommend it be run. + Also, by default Privoxy listens + to requests from "localhost" only. +
+
+ The server aspect of Privoxy is + not itself directly exposed to the Internet in this configuration. + If you want to have Privoxy serve + as a LAN proxy, this will have to be opened up to allow for LAN + requests. In this case, we'd recommend you specify only the LAN + gateway address, e.g. 192.168.1.1, in the main Privoxy configuration file and check all access control and security options. All LAN hosts can + then use this as their proxy address in the browser proxy + configuration, but Privoxy will + not listen on any external interfaces. ACLs can be defined in + addition, and using a firewall is always good too. Better safe than + sorry. +
+
+
+
+ 4.17. Can I temporarily disable Privoxy? +
+
+ Privoxy doesn't have a transparent + proxy mode, but you can toggle off blocking and content filtering. +
+
+ The easiest way to do that is to point your browser to the remote + toggle URL: http://config.privoxy.org/toggle. +
+
+ See the Bookmarklets section of the User + Manual for an easy way to access this feature. Note that this + is a feature that may need to be enabled in the main config file. +
+
+
+
+ 4.18. When "disabled" is Privoxy totally out of the + picture? +
+
+ No, this just means all optional filtering and actions are + disabled. Privoxy is still acting + as a proxy, but just doing less of the things that Privoxy would normally be expected to do. It + is still a "middle-man" in the + interaction between your browser and web sites. See below to bypass + the proxy. +
+
+
+
+ 4.19. How can I tell Privoxy to totally ignore + certain sites? +
+
+ Bypassing a proxy, or proxying based on arbitrary criteria, is + purely a browser configuration issue, not a Privoxy issue. Modern browsers typically do + have settings for not proxying certain sites. Check your browser's + help files. +
+
+
+
+ 4.20. My logs show Privoxy "crunches" ads, but also its own internal CGI pages. + What is a "crunch"? +
+
+ A "crunch" simply means Privoxy intercepted something, nothing more. Often this is + indeed ads or banners, but Privoxy + uses the same mechanism for trapping requests for its own internal + pages. For instance, a request for Privoxy's configuration page at: http://config.privoxy.org, is intercepted (i.e. it does + not go out to the 'net), and the familiar CGI configuration is + returned to the browser, and the log consequently will show a "crunch". +
+
+ Since version 3.0.7, Privoxy will also log the crunch reason. If + you are using an older version you might want to upgrade. +
+
+
+
+ 4.21. Can Privoxy affect files that I download + from a webserver? FTP server? +
+
+ From the webserver's perspective, there is no difference between + viewing a document (i.e. a page), and downloading a file. The same + is true of Privoxy. If there is a + match for a block pattern, it will still be blocked, and of + course this is obvious. +
+
+ Filtering is potentially more of a concern since the results are + not always so obvious, and the effects of filtering are there + whether the file is simply viewed, or downloaded. And potentially + whether the content is some obnoxious advertisement, or Mr. Jimmy's + latest/greatest source code jewel. Of course, one of these + presumably is "bad" content that we + don't want, and the other is "good" + content that we do want. Privoxy + is blind to the differences, and can only distinguish "good from bad" by the configuration parameters + we give it. +
+
+ Privoxy knows the differences in + files according to the "Content Type" as + reported by the webserver. If this is reported accurately (e.g. + "application/zip" for a zip archive), + then Privoxy knows to ignore these + where appropriate. Privoxy + potentially can filter HTML as well as plain text documents, + subject to configuration parameters of course. Also, documents that + are of an unknown type (generally assumed to be "text/plain") can be filtered, as will those that + might be incorrectly reported by the webserver. If such a file is a + downloaded file that is intended to be saved to disk, then any + content that might have been altered by filtering, will be saved + too, for these (probably rare) cases. +
+
+ Note that versions later than 3.0.2 do NOT filter document types + reported as "text/plain". Prior to this, + Privoxy did filter this document + type. +
+
+ In short, filtering is "ON" if a) the + content type as reported by the webserver is appropriate and b) the + configuration allows it (or at least does not disallow it). That's + it. There is no magic cookie anywhere to say this is "good" and this is "bad". + It's the configuration that lets it all happen or not. +
+
+ If you download text files, you probably do not want these to be + filtered, particularly if the content is source code, or other + critical content. Source code sometimes might be mistaken for + Javascript (i.e. the kind that might open a pop-up window). It is + recommended to turn off filtering for download sites (particularly + if the content may be plain text files and you are using version + 3.0.2 or earlier) in your user.action + file. And also, for any site or page where making any changes at all to the + content is to be avoided. +
+
+ Privoxy does not do FTP at all, + only HTTP and HTTPS (SSL) protocols. +
+
+
+
+ 4.22. I just downloaded a Perl script, and + Privoxy altered it! Yikes, what is wrong! +
+
+ Please read above. +
+
+
+
+ 4.23. Should I continue to use a "HOSTS" file for ad-blocking? +
+
+ One time-tested technique to defeat common ads is to trick the + local DNS system by giving a phony IP address for the ad generator + in the local HOSTS file, typically using + 127.0.0.1, aka localhost. This effectively blocks the ad. +
+
+ There is no reason to use this technique in conjunction with Privoxy. Privoxy does essentially the same thing, much + more elegantly and with much more flexibility. A large HOSTS file, in fact, not only duplicates effort, + but may get in the way and seriously slow down your system. It is + recommended to remove such entries from your HOSTS file. If you think your hosts list is + neglected by Privoxy's + configuration, consider adding your list to your user.action file: +
+
+
+ + +
+
+ { +block } www.ad.example1.com ad.example2.com ads.galore.example.com - etc.example.com
4.24. Where can I find more information about Privoxy -and related issues?
Other references and sites of interest to Privoxy - users:

http://www.privoxy.org/, - the Privoxy Home page. -
-
http://www.privoxy.org/faq/, - the Privoxy FAQ. -
-
http://sourceforge.net/projects/ijbswa/, - the Project Page for Privoxy on - SourceForge. -
-
http://config.privoxy.org/, - the web-based user interface. Privoxy must be - running for this to work. Shortcut: http://p.p/ -
-
http://sourceforge.net/tracker/?group_id=11118&atid=460288, to submit "misses" and other - configuration related suggestions to the developers. -
- -
http://www.junkbusters.com/ht/en/cookies.html, - an explanation how cookies are used to track web users. -
-
http://www.junkbusters.com/ijb.html, - the original Internet Junkbuster. -
- -
http://privacy.net/, a useful site - to check what information about you is leaked while you browse the web. -
-
http://www.squid-cache.org/, a very popular - caching proxy, which is often used together with Privoxy. -
-
http://tor.eff.org/, - Tor can help anonymize web browsing, - web publishing, instant messaging, IRC, SSH, and other applications. -
-
http://www.privoxy.org/developer-manual/, - the Privoxy developer manual. -
4.25. I've noticed that Privoxy changes "Microsoft" to -"MicroSuck"! Why are you manipulating my browsing?
We're not. The text substitutions that you are seeing are disabled - in the default configuration as shipped. You have either manually - activated the "fun" filter which - is clearly labeled "Text replacements for subversive browsing - fun!" or you are using an older Privoxy version and have implicitly - activated it by choosing the "Adventuresome" profile in the - web-based editor. Please upgrade!
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Configuration Troubleshooting
\ No newline at end of file + etc.example.com +
+
+

+ 4.24. Where can I find more information about + Privoxy and related issues? +

+ Other references and sites of interest to Privoxy users: +

+ + + + + + +

+ https://www.privoxy.org/, the Privoxy Home page. +

+ + + + + + +

+ https://www.privoxy.org/faq/, the Privoxy FAQ. +

+ + + + + + +

+ https://www.privoxy.org/developer-manual/, the + Privoxy developer manual. +

+ + + + + + +

+ https://sourceforge.net/projects/ijbswa/, the + Project Page for Privoxy on + SourceForge. +

+ + + + + + +

+ http://config.privoxy.org/, the web-based user + interface. Privoxy must be + running for this to work. Shortcut: http://p.p/ +

+ + + + + + +

+ https://sourceforge.net/tracker/?group_id=11118&atid=460288, + to submit "misses" and other + configuration related suggestions to the developers. +

+ + + + + + +

+ http://www.squid-cache.org/, a popular caching + proxy, which is often used together with Privoxy. +

+ + + + + + +

+ http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/, + Polipo is a caching proxy + with advanced features like pipelining, multiplexing and + caching of partial instances. In many setups it can be used + as Squid replacement. +

+ + + + + + +

+ https://www.torproject.org/, Tor can help anonymize web browsing, web + publishing, instant messaging, IRC, SSH, and other + applications. +

+ 4.25. I've noticed that Privoxy changes "Microsoft" to "MicroSuck"! Why are you manipulating my + browsing? +

+ We're not. The text substitutions that you are seeing are disabled + in the default configuration as shipped. You have either manually + activated the "fun" filter which is clearly labeled "Text replacements for subversive browsing + fun!" or you are using an older Privoxy version and have + implicitly activated it by choosing the "Advanced" profile in the web-based editor. Please + upgrade. +

+ 4.26. Does Privoxy produce "valid" HTML (or XHTML)? +

+ Privoxy generates HTML in both its own "templates", and possibly whenever there are text + substitutions via a Privoxy + filter. While this should always conform to the HTML 4.01 + specifications, it has not been validated against this or any other + standard. +

+ 4.27. How did you manage to get Privoxy + on my computer without my consent? +

+ We didn't. We make Privoxy available for download, but we don't go + around installing it on other people's systems behind their back. + If you discover Privoxy running on your system and are sure you + didn't install it yourself, somebody else did. You may not even be + running the real Privoxy, but maybe something else that only + pretends to be Privoxy, or maybe something that is based on the + real Privoxy, but has been modified. +

+ Lately there have been reports of problems with some kind of + "parental control" software based on Privoxy that came preinstalled + on certain ASUS Netbooks. The problems described are + inconsistent with the behaviour of official Privoxy versions, which + suggests that the preinstalled software may contain vendor + modifications that we don't know about and thus can't debug. +

+ Privoxy's license allows vendor + modifications, but the vendor has to comply with the license, which + involves informing the user about the changes and to make the + changes available under the same license as Privoxy itself. +

+ If you are having trouble with a modified Privoxy version, please + try to talk to whoever made the modifications before reporting the + problem to us. Please also try to convince whoever made the + modifications to talk to us. If you think somebody gave you a + modified Privoxy version without complying to the license, please + let us know. +

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