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40 >Privoxy Frequently Asked Questions</TH
48 HREF="configuration.html"
86 >4.1. How much does <SPAN
89 > slow my browsing down? This
90 has to add extra time to browsing.</H3
92 > How much of an impact depends on many things, including the CPU of the host
93 system, how agressive the configuration is, which specific actions are being triggered, etc.</P
95 > Overall, it should not slow you down any in real terms, and may actually help
96 speed things up since ads, banners and other junk are not typically being displayed.
97 The actual processing time required by <SPAN
101 itself for each page, is relatively small in the overall scheme of things,
102 and happens very quickly. This is typically more than offset by time saved
103 not downloading and rendering ad images (if ad blocking is being used).</P
108 > content via the <TT
111 HREF="../user-manual/actions-file.html#FILTER"
119 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
124 actions will cause a perceived slowdown, since the entire document needs to be buffered
125 before displaying. On very large documents, there may be some impact. How
126 much depends on the page size, the actual definition of the filter(s), etc. See below.
127 Most other actions have little to no impact on speed.</P
136 >4.2. I noticed considerable
137 delays in page requests compared to the old Junkbuster. What's wrong?</H3
142 HREF="../user-manual/actions-file.html#FILTER"
147 such as filtering banners by size, web-bugs etc, or the <TT
150 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
155 action, the entire document must be loaded into memory in order for the filtering
156 mechanism to work, and nothing is sent to the browser during this time.</P
158 > The loading time typically does not really change much in real numbers, but
159 the feeling is different, because most browsers are able to start rendering
160 incomplete content, giving the user a feeling of "it works". This effect is
161 more noticeable on slower dialup connections. Extremely large documents
162 may have some impact on the time to load the page. But the overall difference
163 should be very minimal. If there is a big impact, then probably some other
164 problem is contributing.
167 > Filtering is automatically disabled for inappropriate MIME types. But note
168 that if the web server mis-reports the MIME type, then content that should
169 not be filtered, could be. <SPAN
173 to differentiate filterable content because of the MIME type as reported by
174 the server, or because of some configuration setting that enables/disables
184 >4.3. I just installed <SPAN
188 browsing has slowed to a crawl. What gives?</H3
190 > This should not happen, and for the overwhelming number of users world-wide,
191 it does not happen. I would suspect some inadvertent interaction of software
192 components such as anti-virus software, spyware protectors, personal
193 firewalls or similar components. Try disabling (or uninstalling) these one
194 at a time and see if that helps.</P
203 >4.4. What are "http://config.privoxy.org/" and
207 HREF="http://config.privoxy.org/"
209 >http://config.privoxy.org/</A
214 >'s built-in user interface, and
219 > is a shortcut for it.</P
224 > sits between your web browser and the Internet,
225 it can simply intercept requests for these addresses and answer them with its built-in
231 > This also makes for a good test for your browser configuration: If entering the
233 HREF="http://config.privoxy.org/"
235 >http://config.privoxy.org/</A
237 takes you to a page saying <SPAN
239 >"This is Privoxy ..."</SPAN
241 If you get a page saying <SPAN
243 >"Privoxy is not working"</SPAN
245 your browser didn't use <SPAN
249 hence it could not be intercepted, and you have accessed the <SPAN
256 web site at config.privoxy.org.</P
258 > With recent versions of <SPAN
262 later), the user interface features information on the run time status, the
263 configuration, and even a built-in editor for the <A
264 HREF="../user-manual/actions-file.html"
269 > Note that the built-in URLs from earlier versions of <SPAN
276 >, http://example.com/show-proxy-args and http://i.j.b/,
277 are no longer supported. If you still use such an old version, you should really consider
278 upgrading to 3.0.4.</P
287 >4.5. How can I submit new ads, or report
294 various ways to interact with the developers.</P
303 >4.6. Why doesn't anyone answer my support
306 >Rest assured that it has been read and considered. Why it is not answered,
307 could be for various reasons, including no one has a good answer for it, no
308 one has had time to yet investigate it thorougly, it has been reported
309 numerous times already, or because not enough information was provided to help
310 us help you. Your efforts are not wasted, and we do appreciate them.</P
319 >4.7. How can I hide my IP address?</H3
321 > If you run both the browser and the proxy locally, you cannot hide your IP
325 > or ultimately any other
326 software. The server needs to know your IP address to send the answers back
329 > Fortunately there are many publicly usable anonymous proxies out there, which
330 solve the problem by providing a further level of indirection between you and
331 the web server, shared by many people, and thus letting your requests "drown"
332 in white noise of unrelated requests as far as user tracking is concerned.</P
334 > Most of them will, however, log your IP address and make it available to the
335 authorities in case you abuse that anonymity for criminal purposes. In fact
336 you can't even rule out that some of them only exist to *collect* information
337 on (those suspicious) people with a more than average preference for privacy.</P
339 > You can find a list of anonymous public proxies at <A
340 HREF="http://www.multiproxy.org/anon_proxy.htm"
344 more through Google. A particularly interesting project is the JAP service
345 offered by the Technical University of Dresden (<A
346 HREF="http://anon.inf.tu-dresden.de/index_en.html"
348 >http://anon.inf.tu-dresden.de/index_en.html</A
351 > There is, however, even in the single-machine case the possibility to make the
352 server believe that your machine is in fact a shared proxy serving a large
353 LAN, and we are looking into that.</P
365 > guarantee I am anonymous?</H3
367 > No. Your chances of remaining anonymous are greatly improved, but unless you
368 are an expert on Internet security it would be safest to assume that
369 everything you do on the Web can be traced back to you.</P
374 > can remove various information about you,
381 > more freedom to decide which sites
382 you can trust, and what details you want to reveal. But it's still possible
383 that web sites can find out who you are. Here's one way this can happen.</P
385 > A few browsers disclose the user's email address in certain situations, such
386 as when transferring a file by FTP. <SPAN
390 does not filter FTP. If you need this feature, or are concerned about the
391 mail handler of your browser disclosing your email address, you might
392 consider products such as <SPAN
397 > Browsers available only as binaries could use non-standard headers to give
398 out any information they can have access to: see the manufacturer's license
399 agreement. It's impossible to anticipate and prevent every breach of privacy
400 that might occur. The professionally paranoid prefer browsers available as
401 source code, because anticipating their behavior is easier. Trust the source,
411 >4.9. Might some things break because header information or
412 content is being altered?</H3
414 > Definitely. More and more sites use HTTP header content to decide what to
415 display and how to display it. There is many ways that this can be handled,
416 so having hard and fast rules, is tricky.</P
421 > in particular is often used in this way to identify
422 the browser, and adjust content accordingly. Changing this now (at least not
423 further than removing the OS information) is not recommended, since so many
424 sites do look for it. You may get undesirable results by changing this.</P
426 > For instance, different browsers use different encodings of Russian and Czech
427 characters, certain web servers convert pages on-the-fly according to the
428 User Agent header. Giving a <SPAN
432 operating system or browser manufacturer causes some sites in these languages
433 to be garbled; Surfers to Eastern European sites should change it to
434 something closer. And then some page access counters work by looking at the
438 > header; they may fail or break if unavailable. The
439 weather maps of Intellicast have been blocked by their server when no
443 > or cookie is provided, is another example. (But you
444 can forge both headers without giving information away). There are
445 many other ways things can go wrong when trying to fool a web server.</P
447 > Similar thoughts apply to modifying JavaScript, and, to a lesser degree,
450 > If you have problems with a site, you will have to adjust your configuration
451 accordingly. Cookies are probably the most likely adjustment that may
452 be required, but by no means the only one.</P
468 speed up web browsing?</H3
470 > No, it does not have this ability at all. You want something like
472 HREF="http://www.squid-cache.org/"
475 > for this. And, yes,
476 before you ask, <SPAN
480 with other kinds of proxies like <SPAN
485 HREF="../user-manual/config.html#FORWARDING"
490 HREF="../user-manual/index.html"
503 >4.11. What about as a firewall? Can <SPAN
508 > Not in the way you mean, or in the way a true firewall can.
512 > can help protect your privacy, but not
513 protect you from intrusion attempts. It is, of course, perfectly possible
514 and recommended to use <SPAN
529 >4.12. I have large empty spaces / a checkerboard pattern now where
530 ads used to be. Why?</H3
532 > It would be technically possible eliminate the banners in a way that frees
533 their screen estate in many cases, by doing all banner blocking with filters,
534 i.e. eliminating the whole image references from the HTML pages instead
535 of letting them stay in, and blocking the resulting requests for the
536 banners themselves.</P
538 > But this would consume considerable CPU resources, would likely destroy
539 the layout of many web pages which rely on the banners consuming a certain
540 amount of screen space, and would fail in other cases, where the screen space
541 is reserved e.g. by tables anyway. Also, making the banners disappear without
542 a visual trace complicates troubleshooting.</P
544 > So we won't support this in the default configuration, but you can of course
545 define appropriate filters yourself.</P
557 > filter Secure (HTTPS) URLs?</H3
559 > Since secure HTTP connections are encrypted SSL sessions between your browser
560 and the secure site, and are meant to be reliably <SPAN
567 there is little that <SPAN
570 > can do but hand the raw
571 gibberish data though from one end to the other unprocessed.</P
573 > The only exception to this is blocking by host patterns, as the client needs
577 > the name of the remote server,
581 > can establish the connection.
582 If that name matches a host-only pattern, the connection will be blocked.</P
584 > As far as ad blocking is concerned, this is less of a restriction than it may
585 seem, since ad sources are often identifiable by the host name, and often
586 the banners to be placed in an encrypted page come unencrypted nonetheless
587 for efficiency reasons, which exposes them to the full power of
595 >"Content cookies"</SPAN
596 > (those that are embedded in the actual HTML or
597 JS page content, see <TT
600 HREF="../user-manual/actions-file.html#FILTER-CONTENT-COOKIES"
602 >filter{content-cookies}</A
605 in an SSL transaction will be impossible to block under these conditions.
606 Fortunately, this does not seem to be a very common scenario since most
607 cookies come by traditional means.</P
623 secure is it? Do I need to take any special precautions?</H3
625 > There are no known exploits that might affect
629 >. On Unix-like systems,
633 > can run as a non-privileged
634 user, which is how we recommend it be run. Also, by default
638 > only listens to requests
642 > only. The server aspect of
646 > is not itself directly exposed to the
647 Internet in this configuration. If you want to have
651 > serve as a LAN proxy, this will have to
652 be opened up to allow for LAN requests. In this case, we'd recommend
653 you specify only the LAN gateway address, e.g. 192.168.1.1, in the main
657 > configuration file and check all <A
658 HREF="../user-manual/config.html#ACCESS-CONTROL"
660 >access control and security
662 >. All LAN hosts can then use this as their proxy address
663 in the browser proxy configuration, but <SPAN
667 will not listen on any external interfaces. ACLs can be defined in addition,
668 and using a firewall is always good too. Better safe than sorry.</P
677 >4.15. How can I temporarily disable <SPAN
682 > The easiest way is to access <SPAN
686 browser by using the remote toggle URL: <A
687 HREF="http://config.privoxy.org/toggle"
689 >http://config.privoxy.org/toggle</A
692 HREF="../user-manual/appendix.html#BOOKMARKLETS"
694 >Bookmarklets section</A
699 > for an easy way to access this
716 out of the picture?</H3
718 > No, this just means all filtering and actions are disabled.
722 > is still acting as a proxy, but just not
723 doing any of the things that <SPAN
727 normally be expected to do. It is still a <SPAN
731 the interaction between your browser and web sites.</P
740 >4.17. My logs show <SPAN
747 ads, but also its own CGI pages. What is a <SPAN
765 >, nothing more. Often this is indeed ads or
769 > uses the same mechanism for
770 trapping requests for its own internal pages. For instance, a request for
774 > configuration page at: <A
775 HREF="http://config.privoxy.org"
777 >http://config.privoxy.org</A
779 intercepted (i.e. it does not go out to the 'net), and the familiar CGI
780 configuration is returned to the browser, and the log consequently will show
796 > effect files that I download
797 from a webserver? FTP server?</H3
799 > From the webserver's perspective, there is no difference between
800 viewing a document (i.e. a page), and downloading a file. The same is true of
804 >. If there is a match for a <TT
807 HREF="../user-manual/actions-file.html#BLOCK"
812 it will still be blocked, and of course this is obvious.
815 > Filtering is potentially more of a concern since the results are not always
816 so obvious, and the effects of filtering are there whether the file is simply
817 viewed, or downloaded. And potentially whether the content is some obnoxious
818 advertizement, or Mr. Jimmy's latest/greatest source code jewel. Of course,
819 one of these presumably is <SPAN
822 > content that we don't want, and
826 > content that we do want.
830 > is blind to the differences, and can only
833 >"good from bad"</SPAN
834 > by the configuration parameters
846 > knows the differences in files according
849 >"Document Type"</SPAN
850 > as reported by the webserver. If this is
851 reported accurately (e.g. <SPAN
853 >"application/zip"</SPAN
854 > for a zip archive),
858 > knows to ignore these where
862 > potentially can filter HTML
863 as well as plain text documents, subject to configuration parameters of
864 course. Also, documents that are of an unknown type (generally assumed to be
868 >) can be filtered, as will those that might be
869 incorrectly reported by the webserver. If such a file is a downloaded file
870 that is intended to be saved to disk, then any content that might have been
871 altered by filtering, will be saved too, for these (probably rare) cases.</P
873 > Note that versions later than 3.0.2 do NOT filter document types of
877 >. Prior to this, <SPAN
881 did filter this document type.</P
883 > In short, filtering is <SPAN
886 > if a) the Document Type as reported
887 by the webserver is appropriate <SPAN
893 > b) the configuration
894 allows it (or at least does not disallow it). That's it. There is no magic
895 cookie anywhere to say this is <SPAN
902 >. It's the configuration that let's it all happen or not.</P
904 > If you download text files, you probably do not want these to be filtered,
905 particularly if the content is source code, or other critical content. Source
906 code sometimes might be mistaken for Javascript (i.e. the kind that might
907 open a pop-up window). It is recommended to turn off filtering for download
908 sites (particularly if the content may be plain text files and you are using
909 version 3.0.2 or earlier) in your <TT
913 also, for any site or page where making <SPAN
920 all to the content is to be avoided.</P
925 > does not do FTP at all, only HTTP
926 protocols, so please don't even try.</P
935 >4.19. I just downloaded a Perl script, and <SPAN
939 altered it! Yikes, what is wrong!</H3
941 > Please read above.</P
950 >4.20. Where can I find more information about <SPAN
954 and related issues?</H3
956 > Other references and sites of interest to <SPAN
970 HREF="http://www.privoxy.org/"
972 >http://www.privoxy.org/</A
993 HREF="http://www.privoxy.org/faq/"
995 >http://www.privoxy.org/faq/</A
1016 HREF="http://sourceforge.net/projects/ijbswa/"
1018 >http://sourceforge.net/projects/ijbswa/</A
1020 the Project Page for <SPAN
1025 HREF="http://sourceforge.net"
1044 HREF="http://config.privoxy.org/"
1046 >http://config.privoxy.org/</A
1048 the web-based user interface. <SPAN
1052 running for this to work. Shortcut: <A
1072 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());"
1074 >http://www.privoxy.org/actions/</A
1078 > to the developers.
1095 HREF="http://www.junkbusters.com/ht/en/cookies.html"
1097 >http://www.junkbusters.com/ht/en/cookies.html</A
1099 an explanation how cookies are used to track web users.
1115 HREF="http://www.junkbusters.com/ijb.html"
1117 >http://www.junkbusters.com/ijb.html</A
1119 the original Internet Junkbuster.
1136 HREF="http://privacy.net/analyze/"
1138 >http://privacy.net/analyze/</A
1140 to check what information about you is leaked while you browse the web.
1156 HREF="http://www.squid-cache.org/"
1158 >http://www.squid-cache.org/</A
1160 caching proxy, which is often used together with <SPAN
1179 HREF="http://www.privoxy.org/developer-manual/"
1181 >http://www.privoxy.org/developer-manual/</A
1202 >4.21. I've noticed that Privoxy changes <SPAN
1209 >! Why are you manipulating my browsing?</H3
1211 > We're not. The text substitutions that you are seeing are disabled
1212 in the default configuration as shipped. You have either manually
1220 is clearly labeled <SPAN
1222 >"Text replacements for subversive browsing
1224 > or you have implicitly activated it by choosing the
1227 >"Adventuresome"</SPAN
1228 > profile in the web-based editor (formerly known
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