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35 Privoxy Frequently Asked Questions
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53 <a name="GENERAL">1. General Information</a>
57 <a name="WHO-USES">1.1. Who should give <span class=
58 "APPLICATION">Privoxy</span> a try?</a>
61 Anyone who is interested in security, privacy, or in finer-grained
62 control over their web and Internet experience.
67 <a name="BESTCHOICE">1.2. Is Privoxy the best choice for me?</a>
70 <span class="APPLICATION">Privoxy</span> is certainly a good
71 choice, especially for those who want more control and security.
72 Those with the willingness to read the documentation and the
73 ability to fine-tune their installation will benefit the most.
76 One of <span class="APPLICATION">Privoxy's</span> strengths is that
77 it is highly configurable giving you the ability to completely
78 personalize your installation. Being familiar with, or at least
79 having an interest in learning about <a href=
80 "http://en.wikipedia.org/wiki/Http" target="_top">HTTP</a> and
81 other networking protocols, <a href=
82 "http://en.wikipedia.org/wiki/Html" target="_top">HTML</a>, and <a
83 href="http://en.wikipedia.org/wiki/Regular_expressions" target=
84 "_top"><span class="QUOTE">"Regular Expressions"</span></a> will be
85 a big plus and will help you get the most out of <span class=
86 "APPLICATION">Privoxy</span>. A new installation just includes a
87 very basic configuration. The user should take this as a starting
88 point only, and enhance it as he or she sees fit. In fact, the user
89 is encouraged, and expected to, fine-tune the configuration.
92 Much of <span class="APPLICATION">Privoxy's</span> configuration
93 can be done with a <a href=
94 "http://en.wikipedia.org/wiki/Web_browser" target="_top">Web
95 browser</a>. But there are areas where configuration is done using
96 a <a href="http://en.wikipedia.org/wiki/Text_editors" target=
97 "_top">text editor</a> to edit configuration files. Also note that
98 the web-based action editor doesn't use authentication and should
99 only be enabled in environments where all clients with access to
100 <span class="APPLICATION">Privoxy</span> listening port can be
106 <a name="PROXYMORON">1.3. What is a <span class=
107 "QUOTE">"proxy"</span>? How does Privoxy work?</a>
110 A <a href="http://en.wikipedia.org/wiki/Proxy_server" target=
111 "_top">web proxy</a> is a service, based on a software such as
112 <span class="APPLICATION">Privoxy</span>, that clients (i.e.
113 browsers) can use instead of connecting to web servers directly.
114 The clients then ask the proxy to request objects (web pages,
115 images, movies etc) on their behalf and to forward the data to the
116 clients. It is a <span class="QUOTE">"go-between"</span>. For
117 details, see <a href="http://en.wikipedia.org/wiki/Proxy_server"
118 target="_top">Wikipedia's proxy definition</a>.
121 There are many reasons to use web proxies, such as security
122 (firewalling), efficiency (caching) and others, and there are any
123 number of proxies to accommodate those needs.
126 <span class="APPLICATION">Privoxy</span> is a proxy that is
127 primarily focused on privacy enhancement, ad and junk elimination
128 and freeing the user from restrictions placed on his activities.
129 Sitting between your browser(s) and the Internet, it is in a
130 perfect position to filter outbound personal information that your
131 browser is leaking, as well as inbound junk. It uses a variety of
132 techniques to do this, all of which are under your complete control
133 via the various configuration files and options. Being a proxy also
134 makes it easier to share configurations among multiple browsers
140 <a name="OTHERSTUFF">1.4. Does Privoxy do anything more than ad
144 Yes, ad blocking is but one possible use. There are many, many ways
145 <span class="APPLICATION">Privoxy</span> can be used to sanitize
146 and customize web browsing.
151 <a name="NEWJB">1.5. What is this new version of <span class=
152 "QUOTE">"Junkbuster"</span>?</a>
155 A long time ago, there was the <a href=
156 "http://www.junkbusters.com/ijb.html" target="_top"><span class=
157 "APPLICATION">Internet Junkbuster</span></a>, by Anonymous Coders
158 and <a href="http://www.junkbusters.com/" target="_top">Junkbusters
159 Corporation</a>. This saved many users a lot of pain in the early
160 days of web advertising and user tracking.
163 But the web, its protocols and standards, and with it, the
164 techniques for forcing ads on users, give up autonomy over their
165 browsing, and for tracking them, keeps evolving. Unfortunately, the
166 <span class="APPLICATION">Internet Junkbuster</span> did not.
167 Version 2.0.2, published in 1998, was (and is) the last official <a
168 href="http://www.junkbusters.com/ijbdist.html#release" target=
169 "_top">release</a> available from <a href=
170 "http://www.junkbusters.com" target="_top">Junkbusters
171 Corporation</a>. Fortunately, it had been released under the GNU <a
172 href="http://www.gnu.org/licenses/old-licenses/gpl-2.0.html"
173 target="_top">GPL</a>, which allowed further development by others.
176 So Stefan Waldherr started maintaining an improved version of the
177 software, to which eventually a number of people contributed
178 patches. It could already replace banners with a transparent image,
179 and had a first version of pop-up killing, but it was still very
180 closely based on the original, with all its limitations, such as
181 the lack of HTTP/1.1 support, flexible per-site configuration, or
182 content modification. The last release from this effort was version
183 2.0.2-10, published in 2000.
187 "http://www.privoxy.org/user-manual/copyright.html#AUTHORS" target=
188 "_top">developers</a> picked up the thread, and started turning the
189 software inside out, upside down, and then reassembled it, adding
191 "http://www.privoxy.org/user-manual/introduction.html#FEATURES"
192 target="_top">new features</a> along the way.
195 The result of this is <span class="APPLICATION">Privoxy</span>,
196 whose first stable version, 3.0, was released August, 2002.
201 <a name="AEN85">1.6. Why <span class="QUOTE">"Privoxy"</span>? Why
202 change the name from Junkbuster at all?</a>
205 Though outdated, <a href="http://junkbusters.com/" target=
206 "_top">Junkbusters Corporation</a> continues to offer their
207 original version of the <span class="APPLICATION">Internet
208 Junkbuster</span>, so publishing our <span class=
209 "APPLICATION">Junkbuster</span>-derived software under the same
210 name led to confusion.
213 There are also potential legal complications from our use of the
214 <span class="APPLICATION">Junkbuster</span> name, which is a
215 registered trademark of <a href="http://junkbusters.com/" target=
216 "_top">Junkbusters Corporation</a>. There are, however, no
217 objections from Junkbusters Corporation to the <span class=
218 "APPLICATION">Privoxy</span> project itself, and they, in fact,
219 still share our ideals and goals.
222 The developers also believed that there are so many improvements
223 over the original code, that it was time to make a clean break from
224 the past and make a name in their own right.
227 <span class="APPLICATION">Privoxy</span> is the <span class=
228 "QUOTE">"<span class="emphasis"><i class="EMPHASIS">Privacy
229 Enhancing Proxy</i></span>"</span>. Also, its content modification
230 and junk suppression gives <span class="emphasis"><i class=
231 "EMPHASIS">you</i></span>, the user, more control, more freedom,
232 and allows you to browse your personal and <span class=
233 "QUOTE">"<span class="emphasis"><i class=
234 "EMPHASIS">private</i></span> edition"</span> of the web.
239 <a name="DIFFERS">1.7. How does Privoxy differ from the old
243 <span class="APPLICATION">Privoxy</span> picks up where <span
244 class="APPLICATION">Junkbuster</span> left off. The new <span
245 class="APPLICATION">Privoxy</span> still blocks ads and banners,
246 still manages <a href="http://en.wikipedia.org/wiki/Browser_cookie"
247 target="_top">cookies</a>, and still helps protect your privacy.
248 But, most of these features have been enhanced, and many new ones
249 have been added, all in the same vein.
252 <span class="APPLICATION">Privoxy</span>'s new features include:
259 Supports "Connection: keep-alive". Outgoing connections can be
260 kept alive independently from the client.
265 Supports IPv6, provided the operating system does so too, and
266 the configure script detects it.
271 Supports tagging which allows to change the behaviour based on
272 client and server headers.
277 Can be run as an "intercepting" proxy, which obviates the need
278 to configure browsers individually.
283 Sophisticated actions and filters for manipulating both server
289 Can be chained with other proxies.
294 Integrated browser-based configuration and control utility at
295 <a href="http://config.privoxy.org/" target=
296 "_top">http://config.privoxy.org/</a> (shortcut: <a href=
297 "http://p.p/" target="_top">http://p.p/</a>). Browser-based
298 tracing of rule and filter effects. Remote toggling.
303 Web page filtering (text replacements, removes banners based on
304 size, invisible <span class="QUOTE">"web-bugs"</span> and HTML
310 Modularized configuration that allows for standard settings and
311 user settings to reside in separate files, so that installing
312 updated actions files won't overwrite individual user settings.
317 Support for Perl Compatible Regular Expressions in the
318 configuration files, and a more sophisticated and flexible
319 configuration syntax.
329 Bypass many click-tracking scripts (avoids script redirection).
334 User-customizable HTML templates for most proxy-generated pages
335 (e.g. "blocked" page).
340 Auto-detection and re-reading of config file changes.
345 Most features are controllable on a per-site or per-location
351 Many smaller new features added, limitations and bugs removed.
358 <a name="WHATSANAD">1.8. How does Privoxy know what is an ad, and
362 <span class="APPLICATION">Privoxy</span>'s approach to blocking ads
366 First, there are certain patterns in the <span class="emphasis"><i
367 class="EMPHASIS">locations</i></span> (URLs) of banner images. This
368 applies to both the path (you wouldn't guess how many web sites
369 serve their banners from a directory called <span class=
370 "QUOTE">"banners"</span>!) and the host (blocking the big banner
371 hosting services like doublecklick.net already helps a lot). <span
372 class="APPLICATION">Privoxy</span> takes advantage of this fact by
373 using <a href="../user-manual/actions-file.html#AF-PATTERNS"
374 target="_top">URL patterns</a> to sort out and block the requests
375 for things that sound like they would be ads or banners.
378 Second, banners tend to come in certain <span class="emphasis"><i
379 class="EMPHASIS">sizes</i></span>. But you can't tell the size of
380 an image by its URL without downloading it, and if you do, it's too
381 late to save bandwidth. Therefore, <span class=
382 "APPLICATION">Privoxy</span> also inspects the HTML sources of web
383 pages while they are loaded, and replaces references to images with
384 standard banner sizes by dummy references, so that your browser
385 doesn't request them anymore in the first place.
388 Both of this involves a certain amount of guesswork and is, of
389 course, freely and readily configurable.
394 <a name="AEN163">1.9. Can Privoxy make mistakes? This does not
395 sound very scientific.</a>
398 Actually, it's a black art ;-) And yes, it is always possible to
399 have a broad rule accidentally block or change something by
400 mistake. You will almost surely run into such situations at some
401 point. It is tricky writing rules to cover every conceivable
402 possibility, and not occasionally get false positives.
405 But this should not be a big concern since the <span class=
406 "APPLICATION">Privoxy</span> configuration is very flexible, and
407 includes tools to help identify these types of situations so they
408 can be addressed as needed, allowing you to customize your
409 installation. (<a href="trouble.html#BADSITE">See the
410 Troubleshooting section below</a>.)
415 <a name="AEN169">1.10. Will I have to configure Privoxy before I
419 That depends on your expectations. The default installation should
420 give you a good starting point, and block <span class="emphasis"><i
421 class="EMPHASIS">most</i></span> ads and unwanted content, but many
422 of the more advanced features are off by default, and require you
426 You do have to set up your browser to use <span class=
427 "APPLICATION">Privoxy</span> (see the <a href=
428 "installation.html#FIRSTSTEP">Installation section below</a>).
431 And you will certainly run into situations where there are false
432 positives, or ads not being blocked that you may not want to see.
433 In these cases, you would certainly benefit by customizing <span
434 class="APPLICATION">Privoxy's</span> configuration to more closely
435 match your individual situation. And we encourage you to do this.
436 This is where the real power of <span class=
437 "APPLICATION">Privoxy</span> lies!
442 <a name="LAN">1.11. Can Privoxy run as a server on a network?</a>
445 Yes, <span class="APPLICATION">Privoxy</span> runs as a server
446 already, and can easily be configured to <span class=
447 "QUOTE">"serve"</span> more than one client. See <a href=
448 "configuration.html#LANCONFIG">How can I set up Privoxy to act as a
449 proxy for my LAN</a> below.
454 <a name="BROWSERS2">1.12. My browser does the same things as
455 Privoxy. Why should I use Privoxy at all?</a>
458 Modern browsers do indeed have <span class="emphasis"><i class=
459 "EMPHASIS">some</i></span> of the same functionality as <span
460 class="APPLICATION">Privoxy</span>. Maybe this is adequate for you.
461 But <span class="APPLICATION">Privoxy</span> is very versatile and
462 powerful, and can probably do a number of things your browser just
466 In addition, a proxy is good choice if you use multiple browsers,
467 or have a LAN with multiple computers since <span class=
468 "APPLICATION">Privoxy</span> can run as a server application. This
469 way all the configuration is in one place, and you don't have to
470 maintain a similar configuration for possibly many browsers or
474 Note, however, that it's recommended to leverage both your
475 browser's and <span class="APPLICATION">Privoxy's</span> privacy
476 enhancing features at the same time. While your browser probably
477 lacks some features <span class="APPLICATION">Privoxy</span>
478 offers, it should also be able to do some things more reliable, for
479 example restricting and suppressing JavaScript.
484 <a name="WHYTRUST">1.13. Why should I trust Privoxy?</a>
487 The most important reason is because you have access to <span
488 class="emphasis"><i class="EMPHASIS">everything</i></span>, and you
489 can control everything. You can check every line of every
490 configuration file yourself. You can check every last bit of source
491 code should you desire. And even if you can't read code, there
492 should be some comfort in knowing that other people can, and do
493 read it. You can build the software from scratch, if you want, so
494 that you know the executable is clean, and that it is <span class=
495 "emphasis"><i class="EMPHASIS">yours</i></span>. In fact, we
496 encourage this level of scrutiny. It is one reason we use <span
497 class="APPLICATION">Privoxy</span> ourselves.
502 <a name="LICENSE">1.14. Is there is a license or fee? What about a
503 warranty? Registration?</a>
506 <span class="APPLICATION">Privoxy</span> is free software and
507 licensed under the <a href=
508 "http://www.gnu.org/licenses/old-licenses/gpl-2.0.html" target=
509 "_top">GNU General Public License (GPL) version 2</a>. It is free
510 to use, copy, modify or distribute as you wish under the terms of
511 this license. Please see the <a href="copyright.html">Copyright</a>
512 section for more information on the license and copyright. Or the
513 <tt class="FILENAME">LICENSE</tt> file that should be included.
516 There is <span class="emphasis"><i class="EMPHASIS">no
517 warranty</i></span> of any kind, expressed, implied or otherwise.
518 That is something that would cost real money ;-) There is no
524 <a name="SPYWARE">1.15. Can Privoxy remove spyware? Adware?
528 No, at least not reliably enough to trust it. <span class=
529 "APPLICATION">Privoxy</span> is not designed to be a malware
530 removal tool and the default configuration doesn't even try to
531 filter out any malware.
534 <span class="APPLICATION">Privoxy</span> could help prevent contact
535 from (known) sites that use such tactics with appropriate
536 configuration rules, and thus could conceivably prevent
537 contamination from such sites. However, keeping such a
538 configuration up to date would require a lot of time and effort
539 that would be better spend on keeping your software itself up to
540 date so it doesn't have known vulnerabilities.
545 <a name="OTHERADS">1.16. Can I use Privoxy with other ad-blocking
549 <span class="APPLICATION">Privoxy</span> should work fine with
550 other proxies and other software in general.
553 But it is probably not necessary to use <span class=
554 "APPLICATION">Privoxy</span> in conjunction with other ad-blocking
555 products, and this could conceivably cause undesirable results. It
556 might be better to choose one software or the other and work a
557 little to tweak its configuration to your liking.
560 Note that this is an advice specific to ad blocking.
565 <a name="HELP-THE-DEVELOPERS">1.17. I would like to help you, what
570 <a name="PARTICIPATE">1.17.1. Would you like to participate?</a>
573 Well, we <span class="emphasis"><i class=
574 "EMPHASIS">always</i></span> need help. There is something for
575 everybody who wants to help us. We welcome new developers,
576 packagers, testers, documentation writers or really anyone with a
577 desire to help in any way. You <span class="emphasis"><i class=
578 "EMPHASIS">DO NOT</i></span> need to be a <span class=
579 "QUOTE">"programmer"</span>. There are many other tasks
580 available. In fact, the programmers often can't spend as much
581 time programming because of some of the other, more mundane
582 things that need to be done, like checking the Tracker feedback
583 sections or responding to user questions on the mailing lists.
586 So first thing, subscribe to the <a href=
587 "https://lists.sourceforge.net/lists/listinfo/ijbswa-users"
588 target="_top">Privoxy Users</a> or the <a href=
589 "https://lists.sourceforge.net/lists/listinfo/ijbswa-developers"
590 target="_top">Privoxy Developers</a> mailing list, join the
591 discussion, help out other users, provide general feedback or
592 report problems you noticed.
595 If you intend to help out with the trackers, you also might want
596 to <a href="https://sourceforge.net/account/register.php" target=
597 "_top">get an account on SourceForge.net</a> so we don't confuse
598 you with the other name-less users.
601 We also have a <a href="../developer-manual/index.html" target=
602 "_top">Developer's Manual</a>. While it is partly out of date,
603 it's still worth reading.
607 "http://ijbswa.cvs.sourceforge.net/viewvc/ijbswa/current/TODO?view=markup"
608 target="_top">TODO list</a> may be of interest to you as well.
609 Please let us know if you want to work on one of the items
615 <a name="DONATE">1.17.2. Would you like to donate?</a>
618 <span class="APPLICATION">Privoxy</span> is developed by unpaid
619 volunteers and thus our current running costs are pretty low.
620 Nevertheless, we have plans that will cost money in the future.
621 We would like to get this money through donations made by our
625 <span class="APPLICATION">Privoxy</span> has therefore become an
626 associated project of <a href=
627 "http://www.spi-inc.org/about-spi/about-spi" target=
628 "_top">Software in the Public Interest (SPI)</a>, which allows us
629 to receive tax-deductible donations in most western countries.
632 We intend to use the donations to pay for our domain after
633 transferring it to SPI. Our goal is to make sure there's no
634 single point of failure and the bill gets paid and the site keeps
635 running even if a some of the currently active developers were to
636 suddenly disappear for a while.
639 We would also like to spend some money on more reliable hosting,
640 on hardware to help make sure <span class=
641 "APPLICATION">Privoxy</span> keeps running on platforms the
642 developers currently can't test on, and on technical books to
643 educate our developers about said platforms or to improve their
644 knowledge in general.
647 If you enjoy our software and feel like helping out with a
648 donation, please have a look at <a href=
649 "http://www.spi-inc.org/donations" target="_top">SPI's donation
650 page</a> to see what the options are.
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