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52 <h1 class="SECT1"><a name="MISC" id="MISC">4. Miscellaneous</a></h1>
55 <h3 class="SECT2"><a name="AEN738" id="AEN738">4.1. How much does
56 Privoxy slow my browsing down? This has to add extra time to
59 <p>How much of an impact depends on many things, including the CPU of
60 the host system, how aggressive the configuration is, which specific
61 actions are being triggered, the size of the page, the bandwidth of the
64 <p>Overall, it should not slow you down any in real terms, and may
65 actually help speed things up since ads, banners and other junk are not
66 typically being retrieved and displayed. The actual processing time
67 required by <span class="APPLICATION">Privoxy</span> itself for each
68 page, is relatively small in the overall scheme of things, and happens
69 very quickly. This is typically more than offset by time saved not
70 downloading and rendering ad images and other junk content (if ad
71 blocking is being used).</p>
73 <p><span class="QUOTE">"Filtering"</span> content via the <tt class=
74 "LITERAL"><a href="../user-manual/actions-file.html#FILTER" target=
75 "_top">filter</a></tt> or <tt class="LITERAL"><a href=
76 "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
77 "_top">deanimate-gifs</a></tt> actions may cause a perceived slowdown,
78 since the entire document needs to be buffered before displaying. And
79 on very large documents, filtering may have some measurable impact. How
80 much depends on the page size, the actual definition of the filter(s),
81 etc. See below. Most other actions have little to no impact on
84 <p>Also, when filtering is enabled but zlib support isn't available,
85 compression is often disabled (see <a href=
86 "../user-manual/actions-file.html#PREVENT-COMPRESSION" target=
87 "_top">prevent-compression</a>). This can have an impact on speed as
88 well, although it's probably smaller than you might think. Again, the
89 page size, etc. will determine how much of an impact.</p>
93 <h3 class="SECT2"><a name="LOADINGTIMES" id="LOADINGTIMES">4.2. I
94 notice considerable delays in page requests. What's wrong?</a></h3>
96 <p>If you use any <tt class="LITERAL"><a href=
97 "../user-manual/actions-file.html#FILTER" target="_top">filter</a></tt>
98 action, such as filtering banners by size, web-bugs etc, or the
99 <tt class="LITERAL"><a href=
100 "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
101 "_top">deanimate-gifs</a></tt> action, the entire document must be
102 loaded into memory in order for the filtering mechanism to work, and
103 nothing is sent to the browser during this time.</p>
105 <p>The loading time typically does not really change much in real
106 numbers, but the feeling is different, because most browsers are able
107 to start rendering incomplete content, giving the user a feeling of "it
108 works". This effect is more noticeable on slower dialup connections.
109 Extremely large documents may have some impact on the time to load the
110 page where there is filtering being done. But overall, the difference
111 should be very minimal. If there is a big impact, then probably some
112 other situation is contributing (like anti-virus software).</p>
114 <p>Filtering is automatically disabled for inappropriate MIME types.
115 But note that if the web server mis-reports the MIME type, then content
116 that should not be filtered, could be. <span class=
117 "APPLICATION">Privoxy</span> only knows how to differentiate filterable
118 content because of the MIME type as reported by the server, or because
119 of some configuration setting that enables/disables filtering.</p>
123 <h3 class="SECT2"><a name="CONFIGURL" id="CONFIGURL">4.3. What are
124 "http://config.privoxy.org/" and "http://p.p/"?</a></h3>
126 <p><a href="http://config.privoxy.org/" target=
127 "_top">http://config.privoxy.org/</a> is the address of <span class=
128 "APPLICATION">Privoxy</span>'s built-in user interface, and <a href=
129 "http://p.p/" target="_top">http://p.p/</a> is a shortcut for it.</p>
131 <p>Since <span class="APPLICATION">Privoxy</span> sits between your web
132 browser and the Internet, it can simply intercept requests for these
133 addresses and answer them with its built-in <span class="QUOTE">"web
136 <p>This also makes for a good test for your browser configuration: If
137 entering the URL <a href="http://config.privoxy.org/" target=
138 "_top">http://config.privoxy.org/</a> takes you to a page saying
139 <span class="QUOTE">"This is Privoxy ..."</span>, everything is OK. If
140 you get a page saying <span class="QUOTE">"Privoxy is not
141 working"</span> instead, then your browser didn't use <span class=
142 "APPLICATION">Privoxy</span> for the request, hence it could not be
143 intercepted, and you have accessed the <span class=
144 "emphasis EMPHASIS c2">real</span> web site at config.privoxy.org.</p>
148 <h3 class="SECT2"><a name="NEWADS" id="NEWADS">4.4. How can I submit
149 new ads, or report problems?</a></h3>
151 <p>Please see the <a href="contact.html">Contact section</a> for
152 various ways to interact with the developers.</p>
156 <h3 class="SECT2"><a name="NEWADS2" id="NEWADS2">4.5. If I do submit
157 missed ads, will they be included in future updates?</a></h3>
159 <p>Whether such submissions are eventually included in the <tt class=
160 "FILENAME">default.action</tt> configuration file depends on how
161 significant the issue is. We of course want to address any potential
162 problem with major, high-profile sites such as <i class=
163 "CITETITLE">Google</i>, <i class="CITETITLE">Yahoo</i>, etc. Any site
164 with global or regional reach, has a good chance of being a candidate.
165 But at the other end of the spectrum are any number of smaller,
166 low-profile sites such as for local clubs or schools. Since their reach
167 and impact are much less, they are best handled by inclusion in the
168 user's <tt class="FILENAME">user.action</tt>, and thus would be
169 unlikely to be included.</p>
173 <h3 class="SECT2"><a name="NOONECARES" id="NOONECARES">4.6. Why doesn't
174 anyone answer my support request?</a></h3>
176 <p>Rest assured that it has been read and considered. Why it is not
177 answered, could be for various reasons, including no one has a good
178 answer for it, no one has had time to yet investigate it thoroughly, it
179 has been reported numerous times already, or because not enough
180 information was provided to help us help you. Your efforts are not
181 wasted, and we do appreciate them.</p>
185 <h3 class="SECT2"><a name="IP" id="IP">4.7. How can I hide my IP
188 <p>If you run both the browser and <span class=
189 "APPLICATION">Privoxy</span> locally, you cannot hide your IP address
190 with <span class="APPLICATION">Privoxy</span> or ultimately any other
191 software alone. The server needs to know your IP address so that it
192 knows where to send the responses back.</p>
194 <p>There are many publicly usable "anonymous" proxies out there, which
195 provide a further level of indirection between you and the web
198 <p>However, these proxies are called "anonymous" because you don't need
199 to authenticate, not because they would offer any real anonymity. Most
200 of them will log your IP address and make it available to the
201 authorities in case you violate the law of the country they run in. In
202 fact you can't even rule out that some of them only exist to *collect*
203 information on (those suspicious) people with a more than average
204 preference for privacy.</p>
206 <p>If you want to hide your IP address from most adversaries, you
207 should consider chaining <span class="APPLICATION">Privoxy</span> with
208 <a href="https://www.torproject.org/" target="_top">Tor</a>. The
209 configuration details can be found in <a href="#TOR" target="_top">How
210 do I use <span class="APPLICATION">Privoxy</span> together with
211 <span class="APPLICATION">Tor</span> section</a> just below.</p>
215 <h3 class="SECT2"><a name="AEN803" id="AEN803">4.8. Can Privoxy
216 guarantee I am anonymous?</a></h3>
218 <p>No. Your chances of remaining anonymous are improved, but unless you
219 <a href="#TOR" target="_top">chain <span class=
220 "APPLICATION">Privoxy</span> with <span class=
221 "APPLICATION">Tor</span></a> or a similar proxy and know what you're
222 doing when it comes to configuring the rest of your system, you should
223 assume that everything you do on the Web can be traced back to you.</p>
225 <p><span class="APPLICATION">Privoxy</span> can remove various
226 information about you, and allows <span class=
227 "emphasis EMPHASIS c2">you</span> more freedom to decide which sites
228 you can trust, and what details you want to reveal. But it neither
229 hides your IP address, nor can it guarantee that the rest of the system
230 behaves correctly. There are several possibilities how a web sites can
231 find out who you are, even if you are using a strict <span class=
232 "APPLICATION">Privoxy</span> configuration and chained it with
233 <span class="APPLICATION">Tor</span>.</p>
235 <p>Most of <span class="APPLICATION">Privoxy's</span> privacy-enhancing
236 features can be easily subverted by an insecure browser configuration,
237 therefore you should use a browser that can be configured to only
238 execute code from trusted sites, and be careful which sites you trust.
239 For example there is no point in having <span class=
240 "APPLICATION">Privoxy</span> modify the User-Agent header, if websites
241 can get all the information they want through JavaScript, ActiveX,
244 <p>A few browsers disclose the user's email address in certain
245 situations, such as when transferring a file by FTP. <span class=
246 "APPLICATION">Privoxy</span> does not filter FTP. If you need this
247 feature, or are concerned about the mail handler of your browser
248 disclosing your email address, you might consider products such as
249 <span class="APPLICATION">NSClean</span>.</p>
251 <p>Browsers available only as binaries could use non-standard headers
252 to give out any information they can have access to: see the
253 manufacturer's license agreement. It's impossible to anticipate and
254 prevent every breach of privacy that might occur. The professionally
255 paranoid prefer browsers available as source code, because anticipating
256 their behavior is easier. Trust the source, Luke!</p>
260 <h3 class="SECT2"><a name="AEN821" id="AEN821">4.9. A test site says I
261 am not using a Proxy.</a></h3>
263 <p>Good! Actually, they are probably testing for some other kinds of
264 proxies. Hiding yourself completely would require additional steps.</p>
268 <h3 class="SECT2"><a name="TOR" id="TOR">4.10. How do I use Privoxy
269 together with Tor?</a></h3>
271 <p>Before you configure <span class="APPLICATION">Privoxy</span> to use
272 <a href="https://www.torproject.org/" target="_top">Tor</a>, please
273 follow the <i class="CITETITLE">User Manual</i> chapters <a href=
274 "../user-manual/installation.html" target="_top">2. Installation</a>
275 and <a href="../user-manual/startup.html" target="_top">5. Startup</a>
276 to make sure <span class="APPLICATION">Privoxy</span> itself is setup
279 <p>If it is, refer to <a href=
280 "https://www.torproject.org/documentation.html" target="_top">Tor's
281 extensive documentation</a> to learn how to install <span class=
282 "APPLICATION">Tor</span>, and make sure <span class=
283 "APPLICATION">Tor</span>'s logfile says that <span class="QUOTE">"Tor
284 has successfully opened a circuit"</span> and it <span class=
285 "QUOTE">"looks like client functionality is working"</span>.</p>
287 <p>If either <span class="APPLICATION">Tor</span> or <span class=
288 "APPLICATION">Privoxy</span> isn't working, their combination most
289 likely will neither. Testing them on their own will also help you to
290 direct problem reports to the right audience. If <span class=
291 "APPLICATION">Privoxy</span> isn't working, don't bother the
292 <span class="APPLICATION">Tor</span> developers. If <span class=
293 "APPLICATION">Tor</span> isn't working, don't send bug reports to the
294 <span class="APPLICATION">Privoxy</span> Team.</p>
296 <p>If you verified that <span class="APPLICATION">Privoxy</span> and
297 <span class="APPLICATION">Tor</span> are working, it is time to connect
298 them. As far as <span class="APPLICATION">Privoxy</span> is concerned,
299 <span class="APPLICATION">Tor</span> is just another proxy that can be
300 reached by socks4, socks4a and socks5. Most likely you are interested
301 in <span class="APPLICATION">Tor</span> to increase your anonymity
302 level, therefore you should use socks5, to make sure DNS requests are
303 done through <span class="APPLICATION">Tor</span> and thus invisible to
304 your local network. Using socks4a would work too, but with socks5 you
305 get more precise error messages.</p>
307 <p>Since <span class="APPLICATION">Privoxy</span> 3.0.5, its <a href=
308 "../user-manual/config.html" target="_top">main configuration file</a>
309 is already prepared for <span class="APPLICATION">Tor</span>, if you
310 are using a default <span class="APPLICATION">Tor</span> configuration
311 and run it on the same system as <span class=
312 "APPLICATION">Privoxy</span>, you just have to edit the <a href=
313 "../user-manual/config.html#FORWARDING" target="_top">forwarding
314 section</a> and uncomment the line:</p>
316 <table class="c3" border="0" width="100%">
320 # forward-socks5 / 127.0.0.1:9050 .
327 <p>This is enough to reach the Internet, but additionally you might
328 want to uncomment the following forward rules, to make sure your local
329 network is still reachable through Privoxy:</p>
331 <table class="c3" border="0" width="100%">
335 # forward 192.168.*.*/ .
336 # forward 10.*.*.*/ .
337 # forward 127.*.*.*/ .
344 <p>Unencrypted connections to systems in these address ranges will be
345 as (un)secure as the local network is, but the alternative is that your
346 browser can't reach the network at all. Then again, that may actually
347 be desired and if you don't know for sure that your browser has to be
348 able to reach the local network, there's no reason to allow it.</p>
350 <p>If you want your browser to be able to reach servers in your local
351 network by using their names, you will need additional exceptions that
354 <table class="c3" border="0" width="100%">
358 # forward localhost/ .
365 <p>Save the modified configuration file and open <a href=
366 "http://config.privoxy.org/show-status" target=
367 "_top">http://config.privoxy.org/show-status/</a> in your browser,
368 confirm that <span class="APPLICATION">Privoxy</span> has reloaded its
369 configuration and that there are no other forward lines, unless you
370 know that you need them. If everything looks good, refer to <a href=
371 "https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#IsMyConnectionPrivate"
372 target="_top">Tor Faq 4.2</a> to learn how to verify that you are
373 really using <span class="APPLICATION">Tor</span>.</p>
375 <p>Afterward, please take the time to at least skim through the rest of
376 <span class="APPLICATION">Tor's</span> documentation. Make sure you
377 understand what <span class="APPLICATION">Tor</span> does, why it is no
378 replacement for application level security, and why you probably don't
379 want to use it for unencrypted logins.</p>
383 <h3 class="SECT2"><a name="AEN877" id="AEN877">4.11. Might some things
384 break because header information or content is being altered?</a></h3>
386 <p>Definitely. It is common for sites to use browser type, browser
387 version, HTTP header content, and various other techniques in order to
388 dynamically decide what to display and how to display it. What you see,
389 and what I see, might be very different. There are many, many ways that
390 this can be handled, so having hard and fast rules, is tricky.</p>
392 <p>The <span class="QUOTE">"User-Agent"</span> is sometimes used in
393 this way to identify the browser, and adjust content accordingly.</p>
395 <p>Also, different browsers use different encodings of non-English
396 characters, certain web servers convert pages on-the-fly according to
397 the User Agent header. Giving a <span class="QUOTE">"User Agent"</span>
398 with the wrong operating system or browser manufacturer causes some
399 sites in these languages to be garbled; Surfers to Eastern European
400 sites should change it to something closer. And then some page access
401 counters work by looking at the <span class="QUOTE">"Referer"</span>
402 header; they may fail or break if unavailable. The weather maps of
403 Intellicast have been blocked by their server when no <span class=
404 "QUOTE">"Referer"</span> or cookie is provided, is another example.
405 (But you can forge both headers without giving information away). There
406 are many other ways things can go wrong when trying to fool a web
407 server. The results of which could inadvertently cause pages to load
408 incorrectly, partially, or even not at all. And there may be no obvious
409 clues as to just what went wrong, or why. Nowhere will there be a
410 message that says <span class="QUOTE">"<span class=
411 "emphasis EMPHASIS c2">Turn off <tt class="LITERAL">fast-redirects</tt>
412 or else!</span> "</span></p>
414 <p>Similar thoughts apply to modifying JavaScript, and, to a lesser
415 degree, HTML elements.</p>
417 <p>If you have problems with a site, you will have to adjust your
418 configuration accordingly. Cookies are probably the most likely
419 adjustment that may be required, but by no means the only one.</p>
423 <h3 class="SECT2"><a name="AEN891" id="AEN891">4.12. Can Privoxy act as
424 a <span class="QUOTE">"caching"</span> proxy to speed up web
427 <p>No, it does not have this ability at all. You want something like
428 <a href="http://www.squid-cache.org/" target="_top">Squid</a> or
429 <a href="http://www.pps.jussieu.fr/~jch/software/polipo/" target=
430 "_top">Polipo</a> for this. And, yes, before you ask, <span class=
431 "APPLICATION">Privoxy</span> can co-exist with other kinds of proxies
432 like <span class="APPLICATION">Squid</span>. See the <a href=
433 "../user-manual/config.html#FORWARDING" target="_top">forwarding
434 chapter</a> in the <a href="../user-manual/index.html" target=
435 "_top">user manual</a> for details.</p>
439 <h3 class="SECT2"><a name="AEN901" id="AEN901">4.13. What about as a
440 firewall? Can Privoxy protect me?</a></h3>
442 <p>Not in the way you mean, or in the way some firewall vendors claim
443 they can. <span class="APPLICATION">Privoxy</span> can help protect
444 your privacy, but can't protect your system from intrusion attempts. It
445 is, of course, perfectly possible to use <span class=
446 "emphasis EMPHASIS c2">both</span>.</p>
450 <h3 class="SECT2"><a name="AEN906" id="AEN906">4.14. I have large empty
451 spaces / a checkerboard pattern now where ads used to be. Why?</a></h3>
453 <p>It is technically possible to eliminate banners and ads in a way
454 that frees their allocated page space. This could easily be done by
455 blocking with <span class="APPLICATION">Privoxy's</span> filters, and
456 eliminating the <span class="emphasis EMPHASIS c2">entire</span> image
457 references from the HTML page source.</p>
459 <p>But, this would consume considerably more CPU resources (IOW, slow
460 things down), would likely destroy the layout of some web pages which
461 rely on the banners utilizing a certain amount of page space, and might
462 fail in other cases, where the screen space is reserved (e.g. by HTML
463 tables for instance). Also, making ads and banners disappear without
464 any trace complicates troubleshooting, and would sooner or later be
467 <p>The better alternative is to instead let them stay, and block the
468 resulting requests for the banners themselves as is now the case. This
469 leaves either empty space, or the familiar checkerboard pattern.</p>
471 <p>So the developers won't support this in the default configuration,
472 but you can of course define appropriate filters yourself to achieve
477 <h3 class="SECT2"><a name="AEN914" id="AEN914">4.15. How can Privoxy
478 filter Secure (HTTPS) URLs?</a></h3>
480 <p>Since secure HTTP connections are encrypted SSL sessions between
481 your browser and the secure site, and are meant to be reliably
482 <span class="emphasis EMPHASIS c2">secure</span>, there is little that
483 <span class="APPLICATION">Privoxy</span> can do but hand the raw
484 gibberish data though from one end to the other unprocessed.</p>
486 <p>The only exception to this is blocking by host patterns, as the
487 client needs to tell <span class="APPLICATION">Privoxy</span> the name
488 of the remote server, so that <span class="APPLICATION">Privoxy</span>
489 can establish the connection. If that name matches a host-only pattern,
490 the connection will be blocked.</p>
492 <p>As far as ad blocking is concerned, this is less of a restriction
493 than it may seem, since ad sources are often identifiable by the host
494 name, and often the banners to be placed in an encrypted page come
495 unencrypted nonetheless for efficiency reasons, which exposes them to
496 the full power of <span class="APPLICATION">Privoxy</span>'s ad
499 <p><span class="QUOTE">"Content cookies"</span> (those that are
500 embedded in the actual HTML or JS page content, see <tt class=
502 "../user-manual/actions-file.html#FILTER-CONTENT-COOKIES" target=
503 "_top">filter{content-cookies}</a></tt>), in an SSL transaction will be
504 impossible to block under these conditions. Fortunately, this does not
505 seem to be a very common scenario since most cookies come by
506 traditional means.</p>
510 <h3 class="SECT2"><a name="AEN928" id="AEN928">4.16. Privoxy runs as a
511 <span class="QUOTE">"server"</span>. How secure is it? Do I need to
512 take any special precautions?</a></h3>
514 <p>On Unix-like systems, <span class="APPLICATION">Privoxy</span> can
515 run as a non-privileged user, which is how we recommend it be run.
516 Also, by default <span class="APPLICATION">Privoxy</span> listens to
517 requests from <span class="QUOTE">"localhost"</span> only.</p>
519 <p>The server aspect of <span class="APPLICATION">Privoxy</span> is not
520 itself directly exposed to the Internet in this configuration. If you
521 want to have <span class="APPLICATION">Privoxy</span> serve as a LAN
522 proxy, this will have to be opened up to allow for LAN requests. In
523 this case, we'd recommend you specify only the LAN gateway address,
524 e.g. 192.168.1.1, in the main <span class="APPLICATION">Privoxy</span>
525 configuration file and check all <a href=
526 "../user-manual/config.html#ACCESS-CONTROL" target="_top">access
527 control and security options</a>. All LAN hosts can then use this as
528 their proxy address in the browser proxy configuration, but
529 <span class="APPLICATION">Privoxy</span> will not listen on any
530 external interfaces. ACLs can be defined in addition, and using a
531 firewall is always good too. Better safe than sorry.</p>
535 <h3 class="SECT2"><a name="TURNOFF" id="TURNOFF">4.17. Can I
536 temporarily disable Privoxy?</a></h3>
538 <p><span class="APPLICATION">Privoxy</span> doesn't have a transparent
539 proxy mode, but you can toggle off blocking and content filtering.</p>
541 <p>The easiest way to do that is to point your browser to the remote
542 toggle URL: <a href="http://config.privoxy.org/toggle" target=
543 "_top">http://config.privoxy.org/toggle</a>.</p>
545 <p>See the <a href="../user-manual/appendix.html#BOOKMARKLETS" target=
546 "_top">Bookmarklets section</a> of the <i class="CITETITLE">User
547 Manual</i> for an easy way to access this feature. Note that this is a
548 feature that may need to be enabled in the main <tt class=
549 "FILENAME">config</tt> file.</p>
553 <h3 class="SECT2"><a name="REALLYOFF" id="REALLYOFF">4.18. When
554 <span class="QUOTE">"disabled"</span> is Privoxy totally out of the
557 <p>No, this just means all optional filtering and actions are disabled.
558 <span class="APPLICATION">Privoxy</span> is still acting as a proxy,
559 but just doing less of the things that <span class=
560 "APPLICATION">Privoxy</span> would normally be expected to do. It is
561 still a <span class="QUOTE">"middle-man"</span> in the interaction
562 between your browser and web sites. See below to bypass the proxy.</p>
566 <h3 class="SECT2"><a name="TURNOFF2" id="TURNOFF2">4.19. How can I tell
567 Privoxy to totally ignore certain sites?</a></h3>
569 <p>Bypassing a proxy, or proxying based on arbitrary criteria, is
570 purely a browser configuration issue, not a <span class=
571 "APPLICATION">Privoxy</span> issue. Modern browsers typically do have
572 settings for not proxying certain sites. Check your browser's help
577 <h3 class="SECT2"><a name="CRUNCH" id="CRUNCH">4.20. My logs show
578 Privoxy <span class="QUOTE">"crunches"</span> ads, but also its own
579 internal CGI pages. What is a <span class=
580 "QUOTE">"crunch"</span>?</a></h3>
582 <p>A <span class="QUOTE">"crunch"</span> simply means <span class=
583 "APPLICATION">Privoxy</span> intercepted <span class=
584 "emphasis EMPHASIS c2">something</span>, nothing more. Often this is
585 indeed ads or banners, but <span class="APPLICATION">Privoxy</span>
586 uses the same mechanism for trapping requests for its own internal
587 pages. For instance, a request for <span class=
588 "APPLICATION">Privoxy's</span> configuration page at: <a href=
589 "http://config.privoxy.org" target=
590 "_top">http://config.privoxy.org</a>, is intercepted (i.e. it does not
591 go out to the 'net), and the familiar CGI configuration is returned to
592 the browser, and the log consequently will show a <span class=
593 "QUOTE">"crunch"</span>.</p>
595 <p>Since version 3.0.7, Privoxy will also log the crunch reason. If you
596 are using an older version you might want to upgrade.</p>
600 <h3 class="SECT2"><a name="DOWNLOADS" id="DOWNLOADS">4.21. Can Privoxy
601 effect files that I download from a webserver? FTP server?</a></h3>
603 <p>From the webserver's perspective, there is no difference between
604 viewing a document (i.e. a page), and downloading a file. The same is
605 true of <span class="APPLICATION">Privoxy</span>. If there is a match
606 for a <tt class="LITERAL"><a href=
607 "../user-manual/actions-file.html#BLOCK" target="_top">block</a></tt>
608 pattern, it will still be blocked, and of course this is obvious.</p>
610 <p>Filtering is potentially more of a concern since the results are not
611 always so obvious, and the effects of filtering are there whether the
612 file is simply viewed, or downloaded. And potentially whether the
613 content is some obnoxious advertisement, or Mr. Jimmy's latest/greatest
614 source code jewel. Of course, one of these presumably is <span class=
615 "QUOTE">"bad"</span> content that we don't want, and the other is
616 <span class="QUOTE">"good"</span> content that we do want. <span class=
617 "APPLICATION">Privoxy</span> is blind to the differences, and can only
618 distinguish <span class="QUOTE">"good from bad"</span> by the
619 configuration parameters <span class="emphasis EMPHASIS c2">we</span>
622 <p><span class="APPLICATION">Privoxy</span> knows the differences in
623 files according to the <span class="QUOTE">"Content Type"</span> as
624 reported by the webserver. If this is reported accurately (e.g.
625 <span class="QUOTE">"application/zip"</span> for a zip archive), then
626 <span class="APPLICATION">Privoxy</span> knows to ignore these where
627 appropriate. <span class="APPLICATION">Privoxy</span> potentially can
628 filter HTML as well as plain text documents, subject to configuration
629 parameters of course. Also, documents that are of an unknown type
630 (generally assumed to be <span class="QUOTE">"text/plain"</span>) can
631 be filtered, as will those that might be incorrectly reported by the
632 webserver. If such a file is a downloaded file that is intended to be
633 saved to disk, then any content that might have been altered by
634 filtering, will be saved too, for these (probably rare) cases.</p>
636 <p>Note that versions later than 3.0.2 do NOT filter document types
637 reported as <span class="QUOTE">"text/plain"</span>. Prior to this,
638 <span class="APPLICATION">Privoxy</span> did filter this document
641 <p>In short, filtering is <span class="QUOTE">"ON"</span> if a) the
642 content type as reported by the webserver is appropriate <span class=
643 "emphasis EMPHASIS c2">and</span> b) the configuration allows it (or at
644 least does not disallow it). That's it. There is no magic cookie
645 anywhere to say this is <span class="QUOTE">"good"</span> and this is
646 <span class="QUOTE">"bad"</span>. It's the configuration that lets it
647 all happen or not.</p>
649 <p>If you download text files, you probably do not want these to be
650 filtered, particularly if the content is source code, or other critical
651 content. Source code sometimes might be mistaken for Javascript (i.e.
652 the kind that might open a pop-up window). It is recommended to turn
653 off filtering for download sites (particularly if the content may be
654 plain text files and you are using version 3.0.2 or earlier) in your
655 <tt class="FILENAME">user.action</tt> file. And also, for any site or
656 page where making <span class="emphasis EMPHASIS c2">any</span> changes
657 at all to the content is to be avoided.</p>
659 <p><span class="APPLICATION">Privoxy</span> does not do FTP at all,
660 only HTTP and HTTPS (SSL) protocols.</p>
664 <h3 class="SECT2"><a name="DOWNLOADS2" id="DOWNLOADS2">4.22. I just
665 downloaded a Perl script, and Privoxy altered it! Yikes, what is
668 <p>Please read above.</p>
672 <h3 class="SECT2"><a name="HOSTSFILE" id="HOSTSFILE">4.23. Should I
673 continue to use a <span class="QUOTE">"HOSTS"</span> file for
674 ad-blocking?</a></h3>
676 <p>One time-tested technique to defeat common ads is to trick the local
677 DNS system by giving a phony IP address for the ad generator in the
678 local <tt class="FILENAME">HOSTS</tt> file, typically using <tt class=
679 "LITERAL">127.0.0.1</tt>, aka <tt class="LITERAL">localhost</tt>. This
680 effectively blocks the ad.</p>
682 <p>There is no reason to use this technique in conjunction with
683 <span class="APPLICATION">Privoxy</span>. <span class=
684 "APPLICATION">Privoxy</span> does essentially the same thing, much more
685 elegantly and with much more flexibility. A large <tt class=
686 "FILENAME">HOSTS</tt> file, in fact, not only duplicates effort, but
687 may get in the way and seriously slow down your system. It is
688 recommended to remove such entries from your <tt class=
689 "FILENAME">HOSTS</tt> file. If you think your hosts list is neglected
690 by <span class="APPLICATION">Privoxy's</span> configuration, consider
691 adding your list to your <tt class="FILENAME">user.action</tt>
694 <table class="c3" border="0" width="100%">
701 ads.galore.example.com
710 <h3 class="SECT2"><a name="SEEALSO" id="SEEALSO">4.24. Where can I find
711 more information about Privoxy and related issues?</a></h3>
713 <p>Other references and sites of interest to <span class=
714 "APPLICATION">Privoxy</span> users:</p>
719 <td><a href="http://www.privoxy.org/" target=
720 "_top">http://www.privoxy.org/</a>, the <span class=
721 "APPLICATION">Privoxy</span> Home page.</td>
729 <td><a href="http://www.privoxy.org/faq/" target=
730 "_top">http://www.privoxy.org/faq/</a>, the <span class=
731 "APPLICATION">Privoxy</span> FAQ.</td>
739 <td><a href="http://www.privoxy.org/developer-manual/" target=
740 "_top">http://www.privoxy.org/developer-manual/</a>, the
741 <span class="APPLICATION">Privoxy</span> developer manual.</td>
749 <td><a href="https://sourceforge.net/projects/ijbswa/" target=
750 "_top">https://sourceforge.net/projects/ijbswa/</a>, the Project
751 Page for <span class="APPLICATION">Privoxy</span> on <a href=
752 "http://sourceforge.net" target="_top">SourceForge</a>.</td>
760 <td><a href="http://config.privoxy.org/" target=
761 "_top">http://config.privoxy.org/</a>, the web-based user
762 interface. <span class="APPLICATION">Privoxy</span> must be
763 running for this to work. Shortcut: <a href="http://p.p/" target=
764 "_top">http://p.p/</a></td>
773 "https://sourceforge.net/tracker/?group_id=11118&atid=460288"
775 "_top">https://sourceforge.net/tracker/?group_id=11118&atid=460288</a>,
776 to submit <span class="QUOTE">"misses"</span> and other
777 configuration related suggestions to the developers.</td>
785 <td><a href="http://www.junkbusters.com/ht/en/cookies.html"
786 target="_top">http://www.junkbusters.com/ht/en/cookies.html</a>,
787 an explanation how cookies are used to track web users.</td>
795 <td><a href="http://www.junkbusters.com/ijb.html" target=
796 "_top">http://www.junkbusters.com/ijb.html</a>, the original
797 Internet Junkbuster.</td>
805 <td><a href="http://www.squid-cache.org/" target=
806 "_top">http://www.squid-cache.org/</a>, a popular caching proxy,
807 which is often used together with <span class=
808 "APPLICATION">Privoxy</span>.</td>
816 <td><a href="http://www.pps.jussieu.fr/~jch/software/polipo/"
818 "_top">http://www.pps.jussieu.fr/~jch/software/polipo/</a>,
819 <span class="APPLICATION">Polipo</span> is a caching proxy with
820 advanced features like pipelining, multiplexing and caching of
821 partial instances. In many setups it can be used as <span class=
822 "APPLICATION">Squid</span> replacement.</td>
830 <td><a href="https://www.torproject.org/" target=
831 "_top">https://www.torproject.org/</a>, <span class=
832 "APPLICATION">Tor</span> can help anonymize web browsing, web
833 publishing, instant messaging, IRC, SSH, and other
841 <h3 class="SECT2"><a name="MICROSUCK" id="MICROSUCK">4.25. I've noticed
842 that Privoxy changes <span class="QUOTE">"Microsoft"</span> to
843 <span class="QUOTE">"MicroSuck"</span>! Why are you manipulating my
846 <p>We're not. The text substitutions that you are seeing are disabled
847 in the default configuration as shipped. You have either manually
848 activated the <span class="QUOTE">"<tt class="LITERAL">fun</tt>"</span>
849 filter which is clearly labeled <span class="QUOTE">"Text replacements
850 for subversive browsing fun!"</span> or you are using an older Privoxy
851 version and have implicitly activated it by choosing the <span class=
852 "QUOTE">"Advanced"</span> profile in the web-based editor. Please
857 <h3 class="SECT2"><a name="VALID" id="VALID">4.26. Does Privoxy produce
858 <span class="QUOTE">"valid"</span> HTML (or XHTML)?</a></h3>
860 <p>Privoxy generates HTML in both its own <span class=
861 "QUOTE">"templates"</span>, and possibly whenever there are text
862 substitutions via a <span class="APPLICATION">Privoxy</span> filter.
863 While this should always conform to the HTML 4.01 specifications, it
864 has not been validated against this or any other standard.</p>
868 <h3 class="SECT2"><a name="SURPRISE-PRIVOXY" id=
869 "SURPRISE-PRIVOXY">4.27. How did you manage to get Privoxy on my
870 computer without my consent?</a></h3>
872 <p>We didn't. We make Privoxy available for download, but we don't go
873 around installing it on other people's systems behind their back. If
874 you discover Privoxy running on your system and are sure you didn't
875 install it yourself, somebody else did. You may not even be running the
876 real Privoxy, but maybe something else that only pretends to be
877 Privoxy, or maybe something that is based on the real Privoxy, but has
880 <p>Lately there have been reports of problems with some kind of Privoxy
881 versions that come preinstalled on some Netbooks. Some of the problems
882 described are inconsistent with the behaviour of official Privoxy
883 versions, which suggests that the preinstalled software may contain
884 vendor modifications that we don't know about and thus can't debug.</p>
886 <p>Privoxy's <a href="copyright.html">license</a> allows vendor
887 modifications, but the vendor has to comply with the license, which
888 involves informing the user about the changes and to make the changes
889 available under the same license as Privoxy itself.</p>
891 <p>If you are having trouble with a modified Privoxy version, please
892 try to talk to whoever made the modifications before reporting the
893 problem to us. Please also try to convince whoever made the
894 modifications to talk to us. If you think somebody gave you a modified
895 Privoxy version without complying to the license, please let us
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