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40 >Privoxy Frequently Asked Questions</TH
48 HREF="configuration.html"
76 NAME="MISC">4. Miscellaneous</H1
82 NAME="AEN528">4.1. How much does <SPAN
85 > slow my browsing down? This
86 has to add extra time to browsing.</H3
88 > It should not slow you down any in real terms, and may actually help
89 speed things up since ads, banners and other junk are not being displayed.
90 The actual processing time required by <SPAN
94 itself for each page, is relatively small in the overall scheme of things,
95 and happens very quickly. This is typically more than offset by time saved
96 not downloading and rendering ad images.</P
101 > content via the <TT
104 HREF="../user-manual/actions-file.html#FILTER"
112 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
117 actions may cause a perceived slowdown, since the entire document needs to be buffered
118 before displaying. See below.</P
125 NAME="LOADINGTIMES">4.2. I noticed considerable
126 delays in page requests compared to the old Junkbuster. What's wrong?</H3
131 HREF="../user-manual/actions-file.html#FILTER"
136 such as filtering banners by size, web-bugs etc, or the <TT
139 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
144 action, the entire document must be loaded into memory in order for the filtering
145 mechanism to work, and nothing is sent to the browser during this time.</P
147 > The loading time does not really change in real numbers, but the feeling is
148 different, because most browsers are able to start rendering incomplete
149 content, giving the user a feeling of "it works". This effect is especially
150 noticeable on slow dialup connections.
153 > Filtering is automatically disabled for inappropriate MIME types. </P
160 NAME="CONFIGURL">4.3. What are "http://config.privoxy.org/" and
164 HREF="http://config.privoxy.org/"
166 >http://config.privoxy.org/</A
171 >'s built-in user interface, and
176 > is a shortcut for it.</P
181 > sits between your web browser and the Internet,
182 it can simply intercept requests for these addresses and answer them with its built-in
188 > This also makes for a good test for your browser configuration: If entering the
190 HREF="http://config.privoxy.org/"
192 >http://config.privoxy.org/</A
194 takes you to a page saying <SPAN
196 >"This is Privoxy.."</SPAN
198 If you get a page saying <SPAN
200 >"Privoxy is not working"</SPAN
202 your browser didn't use <SPAN
206 hence it could not be intercepted, and you have accessed the <SPAN
213 web site at config.privoxy.org.</P
215 > With recent versions of <SPAN
219 later), the user interface features information on the run time status, the
220 configuration, and even a built-in editor for the <A
221 HREF="../user-manual/actions-file.html"
226 > Note that the built-in URLs from earlier versions of <SPAN
233 >, http://example.com/show-proxy-args and http://i.j.b/,
234 are no longer supported. If you still use such an old version, you should really consider
235 upgrading to 3.1.1.</P
242 NAME="BLOCKLIST">4.4. Do you still maintain the blocklists?</H3
244 > No. The patterns for blocking now reside (among other things) in the <A
245 HREF="../user-manual/actions-file.html"
249 actively maintained instead. See next question ...</P
256 NAME="NEWADS">4.5. How can I submit new ads?</H3
258 >Yes, absolutely! Please see the <A
262 how to do that. Please note that you (technically) need the latest
266 > version for this to work.</P
273 NAME="IP">4.6. How can I hide my IP address?</H3
275 > If you run both the browser and the proxy locally, you cannot hide your IP
279 > or any other software. The
280 server needs to know your IP address to send the answers back to you. </P
282 > Fortunately there are many publicly usable anonymous proxies out there, which
283 solve the problem by providing a further level of indirection between you and
284 the web server, shared by many people, and thus letting your requests "drown"
285 in white noise of unrelated requests as far as user tracking is concerned.</P
287 > Most of them will, however, log your IP address and make it available to the
288 authorities in case you abuse that anonymity for criminal purposes. In fact
289 you can't even rule out that some of them only exist to *collect* information
290 on (those suspicious) people with a more than average preference for privacy.</P
292 > You can find a list of anonymous public proxies at <A
293 HREF="http://www.multiproxy.org/anon_list.htm"
297 more through Google. A particularly interesting project is the JAP service
298 offered by the Technical University of Dresden (<A
299 HREF="http://anon.inf.tu-dresden.de/index_en.html"
301 >http://anon.inf.tu-dresden.de/index_en.html</A
304 > There is, however, even in the single-machine case the possibility to make the
305 server believe that your machine is in fact a shared proxy serving a whole big
306 LAN, and we are looking into that.</P
313 NAME="AEN588">4.7. Can <SPAN
316 > guarantee I am anonymous?</H3
318 > No. Your chances of remaining anonymous are greatly improved, but unless you
319 are an expert on Internet security it would be safest to assume that
320 everything you do on the Web can be traced back to you.</P
325 > can remove various information about you,
332 > more freedom to decide which sites
333 you can trust, and what details you want to reveal. But it's still possible
334 that web sites can find out who you are. Here's one way this can happen.</P
336 > A few browsers disclose the user's email address in certain situations, such
337 as when transferring a file by FTP. <SPAN
341 does not filter FTP. If you need this feature, or are concerned about the
342 mail handler of your browser disclosing your email address, you might
343 consider products such as <SPAN
348 > Browsers available only as binaries could use non-standard headers to give
349 out any information they can have access to: see the manufacturer's license
350 agreement. It's impossible to anticipate and prevent every breach of privacy
351 that might occur. The professionally paranoid prefer browsers available as
352 source code, because anticipating their behavior is easier. Trust the source,
360 NAME="AEN599">4.8. Might some things break because header information or
361 content is being altered?</H3
363 > Definitely. More and more sites use HTTP header content to decide what to
364 display and how to display it. There is many ways that this can be handled,
365 so having hard and fast rules, is tricky.</P
370 > in particular is often used in this way to identify
371 the browser, and adjust content accordingly. Changing this now (at least not
372 further than removing the OS information) is not recommended, since so many
373 sites do look for it. You may get undesirable results by changing this.</P
375 > For instance, different browsers use different encodings of Russian and Czech
376 characters, certain web servers convert pages on-the-fly according to the
377 User Agent header. Giving a <SPAN
381 operating system or browser manufacturer causes some sites in these languages
382 to be garbled; Surfers to Eastern European sites should change it to
383 something closer. And then some page access counters work by looking at the
387 > header; they may fail or break if unavailable. The
388 weather maps of Intellicast have been blocked by their server when no
392 > or cookie is provided, is another example. (But you
393 can forge both headers without giving information away). There are
394 many other ways things can go wrong when trying to fool a web server.</P
396 > Similar thoughts apply to modifying JavaScript, and, to a lesser degree,
399 > If you have problems with a site, you will have to adjust your configuration
400 accordingly. Cookies are probably the most likely adjustment that may
401 be required, but by no means the only one.</P
408 NAME="AEN610">4.9. Can <SPAN
415 speed up web browsing?</H3
417 > No, it does not have this ability at all. You want something like
419 HREF="http://www.squid-cache.org/"
422 > for this. And, yes,
423 before you ask, <SPAN
427 with other kinds of proxies like <SPAN
432 HREF="../user-manual/config.html#FORWARDING"
437 HREF="../user-manual/index.html"
448 NAME="AEN620">4.10. What about as a firewall? Can <SPAN
453 > Not in the way you mean, or in the way a true firewall can.
457 > can help protect your privacy, but not
458 protect you from intrusion attempts. It is, of course, perfectly possible
459 and recommended to use <SPAN
472 NAME="AEN626">4.11. I have large empty spaces / a checkerboard pattern now where
473 ads used to be. Why?</H3
475 > It would be technically possible eliminate the banners in a way that frees
476 their screen estate in many cases, by doing all banner blocking with filters,
477 i.e. eliminating the whole image references from the HTML pages instead
478 of letting them stay in, and blocking the resulting requests for the
479 banners themselves.</P
481 > But this would consume considerable CPU resources, would likely destroy
482 the layout of many web pages which rely on the banners consuming a certain
483 amount of screen space, and would fail in other cases, where the screen space
484 is reserved e.g. by tables anyway. Also, making the banners disappear without
485 a visual trace complicates troubleshooting.</P
487 > So we won't support this in the default configuration, but you can of course
488 define appropriate filters yourself.</P
495 NAME="AEN631">4.12. How can <SPAN
498 > filter Secure (HTTPS) URLs?</H3
500 > Since secure HTTP connections are encrypted SSL sessions between your browser
501 and the secure site, and are meant to be reliably <SPAN
508 there is little that <SPAN
511 > can do but hand the raw
512 gibberish data though from one end to the other unprocessed.</P
514 > The only exception to this is blocking by host patterns, as the client needs
518 > the name of the remote server,
522 > can establish the connection.
523 If that name matches a host-only pattern, the connection will be blocked.</P
525 > As far as ad blocking is concerned, this is less of a restriction than it may
526 seem, since ad sources are often identifiable by the host name, and often
527 the banners to be placed in an encrypted page come unencrypted nonetheless
528 for efficiency reasons, which exposes them to the full power of
539 NAME="AEN642">4.13. <SPAN
546 secure is it? Do I need to take any special precautions?</H3
548 > There are no known exploits that might affect
552 >. On Unix-like systems,
556 > can run as a non-privileged
557 user, which is how we recommend it be run. Also, by default
561 > only listens to requests
565 > only. The server aspect of
569 > is not itself directly exposed to the
570 Internet in this configuration. If you want to have
574 > serve as a LAN proxy, this will have to
575 be opened up to allow for LAN requests. In this case, we'd recommend
576 you specify only the LAN gateway address, e.g. 192.168.1.1, in the main
580 > configuration file and check all <A
581 HREF="../user-manual/config.html#ACCESS-CONTROL"
583 >access control and security
585 >. All LAN hosts can then use this as their proxy address
586 in the browser proxy configuration, but <SPAN
590 will not listen on any external interfaces. ACLs can be defined in addition,
591 and using a firewall is always good too. Better safe than sorry.</P
598 NAME="TURNOFF">4.14. How can I temporarily disable <SPAN
603 > The easiest way is to access <SPAN
607 browser by using the remote toggle URL: <A
608 HREF="http://config.privoxy.org/toggle"
610 >http://config.privoxy.org/toggle</A
613 HREF="../user-manual/appendix.html#BOOKMARKLETS"
615 >Bookmarklets section</A
620 > for an easy way to access this
628 NAME="REALLYOFF">4.15. When <SPAN
635 out of the picture?</H3
637 > No, this just means all filtering and actions are disabled.
641 > is still acting as a proxy, but just not
642 doing any of the things that <SPAN
646 normally be expected to do. It is still a <SPAN
650 the interaction between your browser and web sites.</P
657 NAME="CRUNCH">4.16. My logs show <SPAN
664 ads, but also its own CGI pages. What is a <SPAN
682 >, nothing more. Often this is indeed ads or
686 > uses the same mechanism for
687 trapping requests for its own internal pages. For instance, a request for
691 > configuration page at: <A
692 HREF="http://config.privoxy.org"
694 >http://config.privoxy.org</A
696 intercepted (i.e. it does not go out to the 'net), and the familiar CGI
697 configuration is returned to the browser, and the log consequently will show
708 NAME="DOWNLOADS">4.17. Can <SPAN
711 > effect files that I download
712 from a webserver? FTP server?</H3
714 > From the webserver's perspective, there is no difference between
715 viewing a document (i.e. a page), and downloading a file. The same is true of
719 >. If there is a match for a <TT
722 HREF="../user-manual/actions-file.html#BLOCK"
727 it will still be blocked, and of course this is obvious. Filtering is
728 potentially more of a concern since the results are not always so obvious.</P
733 > knows the differences in files according
736 >"Document Type"</SPAN
737 > as reported by the webserver. If this is
738 reported accurately (e.g. <SPAN
740 >"application/zip"</SPAN
741 > for a zip archive),
745 > knows to ignore these where
746 appropriate. It is possible, however, that documents that are of an unknown
747 type (generally assumed to be <SPAN
750 >) will be filtered, as
751 will those that might be incorrectly reported by the webserver. If such a
752 file is a downloaded file that is intended to be saved to disk, then any
753 content that might have been altered by filtering, will be saved too, for
754 these (probably very rare) cases.</P
759 > does not do FTP at all, only HTTP
767 NAME="SEEALSO">4.18. Where can I find more information about <SPAN
771 and related issues?</H3
773 > Other references and sites of interest to <SPAN
787 HREF="http://www.privoxy.org/"
789 >http://www.privoxy.org/</A
810 HREF="http://www.privoxy.org/faq/"
812 >http://www.privoxy.org/faq/</A
833 HREF="http://sourceforge.net/projects/ijbswa/"
835 >http://sourceforge.net/projects/ijbswa/</A
837 the Project Page for <SPAN
842 HREF="http://sourceforge.net"
861 HREF="http://config.privoxy.org/"
863 >http://config.privoxy.org/</A
865 the web-based user interface. <SPAN
869 running for this to work. Shortcut: <A
889 HREF="javascript:w=Math.floor(screen.width/2);h=Math.floor(screen.height*0.9);void(window.open('http://www.privoxy.org/actions','Feedback','screenx='+w+',width='+w+',height='+h+',scrollbars=yes,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no').focus());"
891 >http://www.privoxy.org/actions/</A
911 HREF="http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ijbswa/contrib/"
913 >http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ijbswa/contrib/</A
915 and fun ideas from <SPAN
934 HREF="http://www.junkbusters.com/ht/en/cookies.html"
936 >http://www.junkbusters.com/ht/en/cookies.html</A
938 an explanation how cookies are used to track web users.
954 HREF="http://www.junkbusters.com/ijb.html"
956 >http://www.junkbusters.com/ijb.html</A
958 the original Internet Junkbuster.
974 HREF="http://www.waldherr.org/junkbuster/"
976 >http://www.waldherr.org/junkbuster/</A
978 Stefan Waldherr's version of Junkbuster, from which <SPAN
998 HREF="http://privacy.net/analyze/"
1000 >http://privacy.net/analyze/</A
1002 to check what information about you is leaked while you browse the web.
1018 HREF="http://www.squid-cache.org/"
1020 >http://www.squid-cache.org/</A
1022 caching proxy, which is often used together with <SPAN
1041 HREF="http://www.privoxy.org/developer-manual/"
1043 >http://www.privoxy.org/developer-manual/</A
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1112 >Troubleshooting</TD