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[privoxy.git] / doc / text / faq.txt

Privoxy Frequently Asked Questions

By: Privoxy Developers

$Id: faq.sgml,v 1.33 2002/03/29 01:31:48 hal9 Exp $

This FAQ gives users and developers alike answers to frequently asked questions
about Privoxy.

Privoxy is a web proxy with advanced filtering capabilities for protecting
privacy, filtering web page content, managing cookies, controlling access, and
removing ads, banners, pop-ups and other obnoxious Internet junk. Privoxy has a
very flexible configuration and can be customized to suit individual needs and
tastes. Privoxy has application for both stand-alone systems and multi-user
networks.

Privoxy is based on the code of the Internet Junkbuster. Junkbuster was
originally written by JunkBusters Corporation, and was released as free
open-source software under the GNU GPL. Stefan Waldherr made many improvements,
and started the SourceForge project to continue development.

You can find the latest version of the document at http://www.privoxy.org/faq/.
Please see the Contact section in the user-manual if you want to contact the
developers.

-------------------------------------------------------------------------------

Table of Contents
1. Frequently Asked Questions
   
    1.1. General Information
       
        1.1.1. What is this new version of Privoxy?
        1.1.2. Why "Privoxy"? Why a name change at all?
        1.1.3. How does Privoxy differ from the old Junkbuster?
        1.1.4. What are some of the new features?
        1.1.5. What is a "proxy"? How does Privoxy work?
        1.1.6. How does Privoxy know what is an ad, and what is not?
        1.1.7. Can Privoxy make mistakes? This does not sound very scientific.
        1.1.8. My browser does the same things as Privoxy. Why should I use
            Privoxy at all?
        1.1.9. Is there is a license or fee? What about a warranty?
            Registration?
        1.1.10. I would like to help you, what do I do?
       
    1.2. Installation
       
        1.2.1. Which browsers are supported by Privoxy?
        1.2.2. Which operating systems are supported?
        1.2.3. Can I install Privoxy over Junkbuster?
        1.2.4. I just installed Privoxy. Is there anything special I have to do
            now?
        1.2.5. What is the proxy address of Privoxy?
        1.2.6. I just installed Privoxy, and nothing is happening. All the ads
            are there. What's wrong?
       
    1.3. Configuration
       
        1.3.1. Can I use my old config files?
        1.3.2. What is an "actions" file?
        1.3.3. The "actions"concept confuses me. Please list some of these
            "actions".
        1.3.4. How are actions files configured? What is the easiest way to do
            this?
        1.3.5. What are the differences between intermediate.action,
            basic.action, etc.?
        1.3.6. Why can I change the configuration with a browser? Does that not
            raise security issues?
        1.3.7. What is "default.filter"?
        1.3.8. How can I set up Privoxy to act as a proxy for my LAN?
        1.3.9. Instead of ads, now I get a checkerboard pattern. I don't want
            to see anything.
        1.3.10. Why would anybody want to see a checkerboard pattern?
        1.3.11. I see large red banners on some pages that say "Blocked". Why
            and how do I get rid of this?
        1.3.12. I cannot see all of the "Blocked" page banner. All I see is a
            bright red square.
        1.3.13. How can I make Privoxy work with other proxies like Squid?
       
    1.4. Miscellaneous
       
        1.4.1. How much does Privoxy slow my browsing down? This has to add
            extra time to browsing.
        1.4.2. I noticed considerable delays in page requests compared to the
            old Junkbuster. What's wrong?
        1.4.3. What is the "http://p.p/"?
        1.4.4. Do you still maintain the blocklists?
        1.4.5. How can I submit new ads?
        1.4.6. How can I hide my IP address?
        1.4.7. Can Privoxy guarantee I am anonymous?
        1.4.8. Might some things break because header information is being
            altered?
        1.4.9. Can Privoxy act as a "caching" proxy to speed up web browsing?
        1.4.10. What about as a firewall? Can Privoxy protect me?
        1.4.11. The Privoxy logo that replaces ads is very blocky and ugly
            looking. Can't a better font be used?
        1.4.12. I have large empty spaces now where ads used to be. Why?
        1.4.13. How can Privoxy filter Secure (HTTPS) URLs?
        1.4.14. Privoxy runs as a "server". How secure is it? Do I need to take
            any special precautions?
        1.4.15. How can I temporarily disable Privoxy?
       
    1.5. Troubleshooting
       
        1.5.1. I just upgraded and am getting "connection refused" with every
            web page?
        1.5.2. I just added a new rule, but the steenkin ad is still getting
            through. How?
        1.5.3. One of my favorite sites does not work with Privoxy. What can I
            do?
        1.5.4. Where can I get help? Report bugs? Feature Requests? Etc?
        1.5.5. What time is it?
       
2. Copyright and History
3. See also

1. Frequently Asked Questions

1.1. General Information

1.1.1. What is this new version of Privoxy?

The original Internet Junkbuster (tm) is a copyrighted product of Junkbusters
Corporation. Development of this effort stopped some time ago as of version
2.0.2. Stefan Waldherr started the ijbswa project on Sourceforge to rekindle
development. Other developers subsequently joined with Stefan, and have since
added many new features, refinements and enhancements. The result of this
effort is Privoxy.

Privoxy started with the same Junkbuster 2.0.2 code base, but has advanced
significantly at this point.

-------------------------------------------------------------------------------

1.1.2. Why "Privoxy"? Why a name change at all?

Privoxy is the "Privacy Enhancing Proxy".

There are possible legal complications from the continued use of the Junkbuster
name, which is a trademark of Junkbusters Corporation. (There are, however, no
objections from Junkbusters Corporation to the Privoxy project itself, and
they, in fact, still share our ideals and goals.)

The developers also believed that there so many changes from the original code,
that it was time to make a clean break from the past and make a name in their
own right, especially now with the pending release of version 3.0. 

-------------------------------------------------------------------------------

1.1.3. How does Privoxy differ from the old Junkbuster?

Privoxy picks up where Junkbuster left off. All the old features remain. The
new Privoxy still blocks ads and banners, still manages cookies, and still
helps protect your privacy. But, these are all enhanced, and many new features
have been added, all in the same vein.

The configuration has changed significantly as well. This is something that
users will notice right off the bat. The "blocklist" file does not exist any
more. This is replaced by "actions" files, such as default.actions. This is
where most of the per site configuration is now.

-------------------------------------------------------------------------------

1.1.4. What are some of the new features?

  * Integrated browser based configuration and control utility (http://p.p).
    Browser-based tracing of rule and filter effects.
   
  * Blocking of annoying pop-up browser windows.
   
  * HTTP/1.1 compliant (most, but not all 1.1 features are supported).
   
  * Support for Perl Compatible Regular Expressions in the configuration files,
    and generally a more sophisticated and flexible configuration syntax over
    previous versions.
   
  * GIF de-animation.
   
  * Web page content filtering (removes banners based on size, invisible
    "web-bugs", JavaScript, pop-ups, status bar abuse, etc.)
   
  * Bypass many click-tracking scripts (avoids script redirection).
   
  * Multi-threaded (POSIX and native threads).
   
  * Auto-detection and re-reading of config file changes.
   
  * User-customizable HTML templates (e.g. 404 error page).
   
  * Improved cookie management features (e.g. session based cookies).
   
  * Improved signal handling, and a true daemon mode (Unix).
   
  * Builds from source on most UNIX-like systems. Packages available for: Linux
    (RedHat, SuSE, or Debian), Windows, Sun Solaris, Mac OSX, OS/2, HP-UX 11
    and AmigaOS.
   
  * In addition, the configuration is much more powerful and versatile
    over-all.
   
-------------------------------------------------------------------------------

1.1.5. What is a "proxy"? How does Privoxy work?

When you connect to a web site with Privoxy, you are really connecting to your
locally running version of Privoxy. Privoxy intercepts your requests for the
web page, and relays that to the "real" web site. The web site sends the HTTP
data stream back to Privoxy, where Privoxy can work its magic before it relays
this data back to your web browser.

Since Privoxy sits between you and the WWW, it is in a position to intercept
and completely manage all web traffic and HTTP content before it gets to your
browser. Privoxy uses various programming methods to do this, all of which is
under your control via the various configuration files and options.

There are many kinds of proxies. Privoxy best fits the "filtering proxy"
category.

-------------------------------------------------------------------------------

1.1.6. How does Privoxy know what is an ad, and what is not?

Privoxy processes all the raw content of every web page. So it reads everything
on each page. It then compares this to the rules as set up in the configuration
files, and looks for any matches to these rules. Privoxy makes heavy use of
"regular expressions". (If you are not familiar with regular expressions, it is
explained briefly in the user manual.) Regular expressions facilitate matching
of one text string against another, using wildcards to build complex patterns.
So Privoxy will typically look for URLs and other content that match certain
key words and expressions as defined in the configuration files. For instance a
URL that contains "/banners", has a high probability of containing ad banners,
and thus would be a prime candidate to have a matching rule.

So Privoxy will look for these kinds of obvious looking culprits. And also,
will use lists of known organizations that specialize in ads. Again, using
complex patterns to match as many potential combinations as possible since
there tend to be many, many variations used by advertisers, and new ones are
being introduced all the time.

-------------------------------------------------------------------------------

1.1.7. Can Privoxy make mistakes? This does not sound very scientific.

Actually, it's a black art ;-) And yes, it is always possible to have a broad
rule accidentally block something by mistake. There is a good chance you may
run into such a situation at some point. It is tricky writing rules to cover
every conceivable possibility, and not occasionally get false positives.

But this should not be a big concern since the Privoxy configuration is very
flexible, and includes tools to help identify these types of situations so they
can be addressed as needed, allowing you to customize your installation. (See
the appendix below.)

-------------------------------------------------------------------------------

1.1.8. My browser does the same things as Privoxy. Why should I use Privoxy at
all?

Modern browsers do indeed have some of the same functionality as Privoxy. Maybe
this is adequate for you. But Privoxy is much more versatile and powerful, and
can do a number of things that browsers just can't.

In addition, a proxy is good choice if you use multiple browsers, or have a LAN
with multiple computers. This way all the configuration is in one place, and
you don't have to maintain a similar configuration for possibly many browsers.

-------------------------------------------------------------------------------

1.1.9. Is there is a license or fee? What about a warranty? Registration?

Privoxy is licensed under the GNU General Public License (GPL). It is free to
use, copy, modify or distribute as you wish under the terms of this license.
See http://www.gnu.org/copyleft/gpl.html for specifics.

There is no warranty of any kind, expressed, implied or otherwise. That is
something that would cost real money ;-) There is no registration either.
Privoxy really is free in every respect!

-------------------------------------------------------------------------------

1.1.10. I would like to help you, what do I do?

1.1.10.1. Money Money Money

We, of course, welcome donations and use the money for domain registering,
regular world-wide get-togethers (hahaha). Anyway, we'll soon describe the
process how to donate money to the team.

-------------------------------------------------------------------------------

1.1.10.2. You want to work with us?

Well, helping the team is always a good idea. We welcome new developers, RPM
gurus or documentation makers. Simply get an account on sourceforge.net and
mail your id to the developer mailing list. Then read the section Quickstart in
the Developer's Manual.

Once we have added you to the team, you'll have write access to the CVS
repository, and together we'll find a suitable task for you.

-------------------------------------------------------------------------------

1.2. Installation

1.2.1. Which browsers are supported by Privoxy?

Any browser that can be configured to use a "proxy", which should be virtually
all browsers. Direct browser support is not necessary since Privoxy runs as a
separate application and just exchanges standard HTML data with your browser.

-------------------------------------------------------------------------------

1.2.2. Which operating systems are supported?

Right now Win32, Mac OSX, OS/2, AmigaOS, Linux, and many flavors of Unix.

Source code is available, so porting to other operating systems, is always a
possibility. 

-------------------------------------------------------------------------------

1.2.3. Can I install Privoxy over Junkbuster?

We recommend you uninstall Junkbuster first to minimize conflicts and
confusion. You may want to save your old configuration files for future
reference. The configuration is substantially changed.

See the user-manual for platform specific installation instructions. [FIXME:
This is meant for after the name change for 3.0!]

Note: Some installers may automatically uninstall Junkbuster, if present!

-------------------------------------------------------------------------------

1.2.4. I just installed Privoxy. Is there anything special I have to do now?

All browsers must be told to use Privoxy as a proxy by specifying the correct
proxy address and port number in the appropriate configuration area for the
browser. See below. Also, you should flush your browser's memory and disk cache
to get rid of any cached items. 

-------------------------------------------------------------------------------

1.2.5. What is the proxy address of Privoxy?

If you set up the Privoxy to run on the computer you browse from (rather than
your ISP's server or some networked computer on a LAN), the proxy will be on
"localhost" (which is the special name used by every computer on the Internet
to refer to itself) and the port will be 8118 (unless you have Privoxy to run
on a different port with the listen-address config option).

When configuring your browser's proxy settings you typically enter the word
"localhost" in the boxes next to "HTTP" and "Secure" (HTTPS) and then the
number "8118" for "port". This tells your browser to send all web requests to
Privoxy instead of directly to the Internet.

Privoxy can also be used to proxy for a Local Area Network. In this case, your
would enter either the IP address of the LAN host where Privoxy is running, or
the equivalent hostname. Port assignment would be same as above.

Privoxy does not currently handle protocols such as FTP, SMTP, IM, IRC, ICQ, or
other Internet protocols.

-------------------------------------------------------------------------------

1.2.6. I just installed Privoxy, and nothing is happening. All the ads are
there. What's wrong?

Did you configure your browser to use Privoxy as a proxy? It does not sound
like it. See above. You might also try flushing the browser's caches to force a
full re-reading of pages. You can verify that Privoxy is running, and your
browser is correctly configured by entering the special URL: http://p.p/. This
should give you a banner that says "This is Privoxy" and access to Privoxy's
internal configuration. If you see this, then you are good to go. If not, the
browser or Privoxy are not set up correctly. 

-------------------------------------------------------------------------------

1.3. Configuration

1.3.1. Can I use my old config files?

There are major changes to Junkbuster configuration from version 2.0.x to 2.9.x
and later. The older files will not work at all. If this is the case, you will
need to re-enter your old data into the new configuration structure. This is
probably also a good recommendation even if upgrading from 2.9.x to 3.x since
there were many minor changes along the way.

-------------------------------------------------------------------------------

1.3.2. What is an "actions" file?

"actions" files are where various actions that Privoxy might take, are
configured. Typically, you would define a set of default actions that apply to
all URLs, then add exceptions to these defaults.

Actions can be defined on a per site basis, or for groups of sites. Actions can
also be grouped together and then applied to one or more sites. There are many
possible actions that might apply to any given site. As an example, if we are
blocking cookies as one of our default actions, but need to accept cookies from
a given site, we would define this in our "actions" file. 

Privoxy comes with several default actions files, with varying degrees of
filtering and blocking, as starting points for your own configuration (see
below).

-------------------------------------------------------------------------------

1.3.3. The "actions"concept confuses me. Please list some of these "actions".

These are all explained in the user-manual. Please refer to that.

-------------------------------------------------------------------------------

1.3.4. How are actions files configured? What is the easiest way to do this?

The easiest way to do this, is to access Privoxy with your web browser at http:
//p.p/, and then select "Edit the actions list" from the selection list. You
can also do this by editing the appropriate file with a text editor.

Please see the user-manual for a detailed explanation of these and other
configuration files, and their various options and syntax.

-------------------------------------------------------------------------------

1.3.5. What are the differences between intermediate.action, basic.action,
etc.?

Configuring Privoxy is not easy. To help you get started, we provide you with
three different default configurations. The following table shows you, which
features are enabled in each configuration.

Table 1. Default Configurations

+--------------------------------------------------------------------------------------+
|Feature             |default.action|basic.action  |intermediate.action|advanced.action|
|--------------------+--------------+--------------+-------------------+---------------|
|ad-filtering        |?             |x             |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|blank image         |?             |x             |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|de-animate GIFs     |?             |x             |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|referer forging     |?             |x             |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|jon's               |?             |x             |x                  |x              |
|+no-cookies-keep    |              |              |                   |               |
|(i.e. session       |              |              |                   |               |
|cookies only)       |              |              |                   |               |
|--------------------+--------------+--------------+-------------------+---------------|
|no-popup windows    |?             |              |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|fast redirects      |?             |              |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|hide-referrer       |?             |              |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|hide-useragent      |?             |              |x                  |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|content-modification|?             |              |                   |x              |
|--------------------+--------------+--------------+-------------------+---------------|
|feature-x           |?             |              |                   |               |
|--------------------+--------------+--------------+-------------------+---------------|
|feature-y           |?             |              |                   |               |
|--------------------+--------------+--------------+-------------------+---------------|
|feature-z           |?             |              |                   |               |
+--------------------------------------------------------------------------------------+

-------------------------------------------------------------------------------

1.3.6. Why can I change the configuration with a browser? Does that not raise
security issues?

What I don't understand, is how I can browser edit the config file as a regular
user, while the whole /etc/privoxy hierarchy belongs to the user "privoxy",
with only 644 perms.

When you use the browser-based editor, Privoxy itself is writing to the config
files. Because Privoxy is running as the user "privoxy", it can update the
config files.

If you don't like this, setting "enable-edit-actions 0" in the config file will
disable the browser-based editor. If you're that paranoid, you should also
consider setting "enable-remote-toggle 0" to prevent browser-based enabling/
disabling of Privoxy.

Note that normally only local users can connect to Privoxy, so this is not
(normally) a security problem.

-------------------------------------------------------------------------------

1.3.7. What is "default.filter"?

The "default.filter" file is used to "filter" any web page content. By
"filtering" we mean it can modify, remove, or change anything on the page,
including HTML tags, and JavaScript. Regular expressions are used to accomplish
this, and operate on a line by line basis. This is potentially a very powerful
feature, but requires some expertise.

If you are familiar with regular expressions, and HTML, you can look at the
provided default.filter with a text editor and see some of things it can be
used for.

Presently, there is no GUI editor option for this part of the configuration,
but you can disable/enable various sections of the included default file with
the "Actions List Editor" from your browser.

-------------------------------------------------------------------------------

1.3.8. How can I set up Privoxy to act as a proxy for my LAN?

By default, Privoxy only responds to requests from localhost. To have it act as
a server for a network, this needs to be changed in the main config file where
the Privoxy configuration is located. In that file is a "listen-address"
option. It may be commented out with a "#" symbol. Make sure it is uncommented,
and assign it the address of the LAN gateway interface, and port number to use:

  listen-address  192.168.1.1:8118                                             
                                                                               

Save the file, and restart Privoxy. Configure all browsers on the network then
to use this address and port number.

-------------------------------------------------------------------------------

1.3.9. Instead of ads, now I get a checkerboard pattern. I don't want to see
anything.

This is a configuration option for images that Privoxy is stopping. You have
the choice of a checkerboard pattern, a transparent 1x1 GIF image (aka
"blank"), or a custom URL of your choice. Note that to fit this category, the
URL must match both the "+image" and "+block" actions.

If you want to see nothing, then change the "+image-blocker" action to
"+image-blocker{blank}". This can be done from the "Edit Actions List"
selection at http://p.p/. Or by hand editing the appropriate actions file. This
will only effect what is defined as "images" though. Also, any URLs that
generate the bright red "Blocked" banner, can be moved to the "+image-blocker"
section for the same reason. 

-------------------------------------------------------------------------------

1.3.10. Why would anybody want to see a checkerboard pattern?

This can be helpful for troubleshooting problems. It might also be good for
anyone new to Privoxy so that they can see if their favorite pages are
displaying correctly, and Privoxy is not inadvertently removing something
important.

-------------------------------------------------------------------------------

1.3.11. I see large red banners on some pages that say "Blocked". Why and how
do I get rid of this?

These are URLs that match something in one of Privoxy's block actions (+block).
It is meant to be a warning so that you know something has been blocked and an
easy way for you to see why. These are handled differently than what has been
defined explicitly as "images" (e.g. ad banners). Depending on the URL itself,
it is sometimes hard for Privoxy to really know whether it is indeed an ad
image or not.

If you want them to be treated as if they were images, so that they can be made
invisible, then move the offending URL from the "+block" section to the
"+imageblock" section of your actions file. Just be forewarned, if make any URL
is made "invisible", you may not have any inkling that something has been
removed from that page.

Alternately, you could modify the "block" HTML template that is used by Privoxy
to display this, and make it something more to your liking.

-------------------------------------------------------------------------------

1.3.12. I cannot see all of the "Blocked" page banner. All I see is a bright
red square.

There is not enough space to fit the entire page. Try right clicking on the
visible, red portion, and select "Show Frame", or equivalent. This will usually
allow you to see the entire Privoxy "Blocked" page, and from there you can see
just what is being blocked, and why.

-------------------------------------------------------------------------------

1.3.13. How can I make Privoxy work with other proxies like Squid?

This can be done. See the user manual, which describes how to do this. 

-------------------------------------------------------------------------------

1.4. Miscellaneous

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

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 being 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.

"Filtering" via the filterfile mechanism may cause a perceived slowdown, since
the entire page is buffered before displaying. See below.

-------------------------------------------------------------------------------

1.4.2. I noticed considerable delays in page requests compared to the old
Junkbuster. What's wrong?

Using the default filtering configuration, I noticed considerable delays in
page requests compared to the old Junkbuster. Loading pages with large contents
seemed to take forever, then suddenly delivering all the content at once.

The whole content must be loaded in order to filter, and nothing is is sent to
the browser during this time. The loading time does not really change 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".

To modify the content of a page (i.e. make frames resizeable again, etc.) and
not just replace ads, Privoxy needs to download the entire page first, do its
content magic and then send the page to the browser.

-------------------------------------------------------------------------------

1.4.3. What is the "http://p.p/"?

Since Privoxy sits between your web browser and the Internet, it can be
programmed to handle certain pages specially.

With recent versions of Privoxy (version 2.9.x), you can get some information
about Privoxy and change some settings by going to http://p.p/ or,
equivalently, http://www.privoxy.org/config/ (Note that p.p is far easier to
type but may not work in some configurations).

These pages are *not* forwarded to a server on the Internet - instead they are
handled by a special web server which is built in to Privoxy.

If you are not running Privoxy, then http://p.p/ will fail, and http://
www.privoxy.org/config/ will return a web page telling you you're not running
Privoxy.

If you have version 2.0.2, then the equivalent is http://example.com/
show-proxy-args (but you get far less information, and you should really
consider upgrading to 2.9.x).

-------------------------------------------------------------------------------

1.4.4. Do you still maintain the blocklists?

No. The format of the blocklists has changed significantly in the versions
2.9.x. Once we have released the new stable version, v3.0, there will again be
blocklists that you can update automatically.

-------------------------------------------------------------------------------

1.4.5. How can I submit new ads?

As of now, please discontinue to submit new ad blocking infos. Once we have
released the new version, there will again be a form on the website, which you
can use to contribute new ads.

-------------------------------------------------------------------------------

1.4.6. How can I hide my IP address?

You cannot hide your IP address with Privoxy or any other software, since the
server needs to know your IP address to send the answer to you.

Fortunately there are many publicly usable anonymous proxies out there, which
solve the problem by providing a further level of indirection between you and
the web server, shared by many people and thus letting your requests "drown" in
white noise of unrelated requests as far as user tracking is concerned.

Most of them will, however, log your IP address and make it available to the
authorities in case you abuse that anonymity for criminal purposes. 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.

You can find a list of anonymous public proxies at multiproxy.org and many more
through Google.

-------------------------------------------------------------------------------

1.4.7. Can Privoxy guarantee I am anonymous?

No. Your chances of remaining anonymous are greatly improved, but unless you
are an expert on Internet security 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. But it's still possible that web sites can
find out who you are. Here's one way this can happen.

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!

-------------------------------------------------------------------------------

1.4.8. Might some things break because header information is being altered?

Definitely. More and more sites use HTTP header content to decide what to
display and how to display it. There is many ways that this can be handled, so
having hard and fast rules, is tricky.

"USER AGENT" in particular is often used in this way to identify the browser,
and adjust content accordingly. Changing this now is not recommended, since so
many sites do look for this. You may get undesirable results by changing this.

For instance, 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. There are
many, many other ways things can go wrong when trying to fool a web server.

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. 

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1.4.9. 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.

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1.4.10. What about as a firewall? Can Privoxy protect me?

Not in the way you mean, or in the way a true firewall can, or a proxy that has
this specific capability. Privoxy can help protect your privacy, but not really
protect you from intrusion attempts.

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1.4.11. The Privoxy logo that replaces ads is very blocky and ugly looking.
Can't a better font be used?

This is not a font problem. The logo is an image that is created by Privoxy on
the fly. So as to not waste memory, the image is rather small. The blockiness
comes when the image is scaled to fill a largish area. There is not much to be
done about this, other than to use one of the other "imageblock" directives:
pattern, blank, or a URL of your choosing.

Given the above problem, we have decided to remove the logo option entirely [as
of v2.9.13].

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1.4.12. I have large empty spaces now where ads used to be. Why?

It would be easy enough to just eliminate this space altogether, rather than
fill it with blank space. But, this would create problems with many pages that
use the overall size of the ad to help organize the page layout and position
the various components of the page where they were intended to be. It is best
left this way.

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1.4.13. How can Privoxy filter Secure (HTTPS) URLs?

This is a limitation since HTTPS transactions are encrypted SSL sessions
between your browser and the secure site, and are meant to be reliably secure
and private. This means that all cookies and HTTP header information are also
encrypted from the time they leave your browser, to the site, and vice versa.
Privoxy does not try to unencrypt this information, so it just passes through
as is. Privoxy can still catch images and ads that are embedded in the SSL
stream though.

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1.4.14. Privoxy runs as a "server". How secure is it? Do I need to take any
special precautions?

There are no known exploits that might effect 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". 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
config file. All LAN hosts can then use this as their proxy address in the
browser proxy configuration. In this way, Privoxy will not listen on any
external ports. Of course, a firewall is always good too. Better safe than
sorry.

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1.4.15. How can I temporarily disable Privoxy?

The easiest way is to access Privoxy with your browser by using the special
URL: http://p.p/ and select "Toggle Privoxy on or off" from that page. 

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1.5. Troubleshooting

1.5.1. I just upgraded and am getting "connection refused" with every web page?

Either Privoxy is not running, or your browser is configured for a different
port than what Privoxy is using.

The old Privoxy (and also Junkbuster) used port 8000 by default. This has been
changed to port 8118 now, due to a conflict with NAS (Network Audio Service),
which uses port 8000. If you haven't, you need to change your browser to the
new port number, or alternately change Privoxy's "listen-address" setting in
the config file used to start Privoxy.

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1.5.2. I just added a new rule, but the steenkin ad is still getting through.
How?

If the ad had been displayed before you added its URL, it will probably be held
in the browser's cache for some time, so it will be displayed without the need
for any request to the server, and Privoxy will not be in the picture. The best
thing to do is try flushing the browser's caches. And then try again.

If this doesn't help, you probably have an error in the rule you applied. Try
pasting the full URL of the offending ad into http://www.privoxy.org/config/
show-url-info and see if any actions match your new rule.

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1.5.3. One of my favorite sites does not work with Privoxy. What can I do?

First verify that it is indeed a Privoxy problem, by disabling Privoxy
filtering and blocking. Go to http://p.p/ and click on "Toggle Privoxy On or
Off", then disable it. Now try that page again. It's probably a good idea to
flush the browser cache as well.

If still a problem, go to "Show which actions apply to a URL and why" from 
http://p.p/ and paste the full URL of the page in question into the prompt. See
which actions are being applied to the URL. Now, armed with this information,
go to "Edit the actions list". Here you should see various sections that have
various Privoxy features disabled for specific sites. Disabled "actions" will
have a "-" (minus sign) in front of them. Add your problem page URL to one of
these sections that looks like it is disabling the feature that is causing the
problem. Re-try the page. There might be some trial and error involved. This is
discussed in a little more detail in the user-manual appendix. 

Alternately, if you are comfortable with a text editor, you can accomplish the
same thing by editing the appropriate "actions" file.

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1.5.4. Where can I get help? Report bugs? Feature Requests? Etc?

Feedback is encouraged, whether good, bad or ugly. Please see the contact page
in the user-manual for details. 

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1.5.5. What time is it?

Time for you to go!

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2. Copyright and History

Please see the user-manual for information on Copyright and History.

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3. See also

Please see the user-manual for others references.