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