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35 <h1 class="SECT1"><a name="MISC" id="MISC">4. Miscellaneous</a></h1>
37 <h3 class="SECT2"><a name="SLOWSME" id="SLOWSME">4.1. How much does
38 Privoxy slow my browsing down? This has to add extra time to
40 <p>How much of an impact depends on many things, including the CPU of
41 the host system, how aggressive the configuration is, which specific
42 actions are being triggered, the size of the page, the bandwidth of the
44 <p>Overall, it should not slow you down any in real terms, and may
45 actually help speed things up since ads, banners and other junk are not
46 typically being retrieved and displayed. The actual processing time
47 required by <span class="APPLICATION">Privoxy</span> itself for each
48 page, is relatively small in the overall scheme of things, and happens
49 very quickly. This is typically more than offset by time saved not
50 downloading and rendering ad images and other junk content (if ad
51 blocking is being used).</p>
52 <p><span class="QUOTE">"Filtering"</span> content via the <tt class=
53 "LITERAL"><a href="../user-manual/actions-file.html#FILTER" target=
54 "_top">filter</a></tt> or <tt class="LITERAL"><a href=
55 "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
56 "_top">deanimate-gifs</a></tt> actions may cause a perceived slowdown,
57 since the entire document needs to be buffered before displaying. And
58 on very large documents, filtering may have some measurable impact. How
59 much depends on the page size, the actual definition of the filter(s),
60 etc. See below. Most other actions have little to no impact on
62 <p>Also, when filtering is enabled but zlib support isn't available,
63 compression is often disabled (see <a href=
64 "../user-manual/actions-file.html#PREVENT-COMPRESSION" target=
65 "_top">prevent-compression</a>). This can have an impact on speed as
66 well, although it's probably smaller than you might think. Again, the
67 page size, etc. will determine how much of an impact.</p>
70 <h3 class="SECT2"><a name="LOADINGTIMES" id="LOADINGTIMES">4.2. I
71 notice considerable delays in page requests. What's wrong?</a></h3>
72 <p>If you use any <tt class="LITERAL"><a href=
73 "../user-manual/actions-file.html#FILTER" target="_top">filter</a></tt>
74 action, such as filtering banners by size, web-bugs etc, or the
75 <tt class="LITERAL"><a href=
76 "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
77 "_top">deanimate-gifs</a></tt> action, the entire document must be
78 loaded into memory in order for the filtering mechanism to work, and
79 nothing is sent to the browser during this time.</p>
80 <p>The loading time typically does not really change much in real
81 numbers, but the feeling is different, because most browsers are able
82 to start rendering incomplete content, giving the user a feeling of "it
83 works". This effect is more noticeable on slower dialup connections.
84 Extremely large documents may have some impact on the time to load the
85 page where there is filtering being done. But overall, the difference
86 should be very minimal. If there is a big impact, then probably some
87 other situation is contributing (like anti-virus software).</p>
88 <p>Filtering is automatically disabled for inappropriate MIME types.
89 But note that if the web server mis-reports the MIME type, then content
90 that should not be filtered, could be. <span class=
91 "APPLICATION">Privoxy</span> only knows how to differentiate filterable
92 content because of the MIME type as reported by the server, or because
93 of some configuration setting that enables/disables filtering.</p>
96 <h3 class="SECT2"><a name="CONFIGURL" id="CONFIGURL">4.3. What are
97 "http://config.privoxy.org/" and "http://p.p/"?</a></h3>
98 <p><a href="http://config.privoxy.org/" target=
99 "_top">http://config.privoxy.org/</a> is the address of <span class=
100 "APPLICATION">Privoxy</span>'s built-in user interface, and <a href=
101 "http://p.p/" target="_top">http://p.p/</a> is a shortcut for it.</p>
102 <p>Since <span class="APPLICATION">Privoxy</span> sits between your web
103 browser and the Internet, it can simply intercept requests for these
104 addresses and answer them with its built-in <span class="QUOTE">"web
106 <p>This also makes for a good test for your browser configuration: If
107 entering the URL <a href="http://config.privoxy.org/" target=
108 "_top">http://config.privoxy.org/</a> takes you to a page saying
109 <span class="QUOTE">"This is Privoxy ..."</span>, everything is OK. If
110 you get a page saying <span class="QUOTE">"Privoxy is not
111 working"</span> instead, then your browser didn't use <span class=
112 "APPLICATION">Privoxy</span> for the request, hence it could not be
113 intercepted, and you have accessed the <span class="emphasis"><i class=
114 "EMPHASIS">real</i></span> web site at config.privoxy.org.</p>
115 <p>Note that config.privoxy.org resolves to a public IP address. If you
116 use config.privoxy.org as ping or traceroute target you will reach the
117 system on the Internet (Privoxy can't intercept ICMP requests). If you
118 want to ping the system Privoxy runs on, you should use its IP address
119 or local DNS name (if it has got one).</p>
122 <h3 class="SECT2"><a name="NEWADS" id="NEWADS">4.4. How can I submit
123 new ads, or report problems?</a></h3>
124 <p>Please see the <a href="contact.html">Contact section</a> for
125 various ways to interact with the developers.</p>
128 <h3 class="SECT2"><a name="NEWADS2" id="NEWADS2">4.5. If I do submit
129 missed ads, will they be included in future updates?</a></h3>
130 <p>Whether such submissions are eventually included in the <tt class=
131 "FILENAME">default.action</tt> configuration file depends on how
132 significant the issue is. We of course want to address any potential
133 problem with major, high-profile sites such as <i class=
134 "CITETITLE">Google</i>, <i class="CITETITLE">Yahoo</i>, etc. Any site
135 with global or regional reach, has a good chance of being a candidate.
136 But at the other end of the spectrum are any number of smaller,
137 low-profile sites such as for local clubs or schools. Since their reach
138 and impact are much less, they are best handled by inclusion in the
139 user's <tt class="FILENAME">user.action</tt>, and thus would be
140 unlikely to be included.</p>
143 <h3 class="SECT2"><a name="NOONECARES" id="NOONECARES">4.6. Why doesn't
144 anyone answer my support request?</a></h3>
145 <p>Rest assured that it has been read and considered. Why it is not
146 answered, could be for various reasons, including no one has a good
147 answer for it, no one has had time to yet investigate it thoroughly, it
148 has been reported numerous times already, or because not enough
149 information was provided to help us help you. Your efforts are not
150 wasted, and we do appreciate them.</p>
153 <h3 class="SECT2"><a name="IP" id="IP">4.7. How can I hide my IP
155 <p>If you run both the browser and <span class=
156 "APPLICATION">Privoxy</span> locally, you cannot hide your IP address
157 with <span class="APPLICATION">Privoxy</span> or ultimately any other
158 software alone. The server needs to know your IP address so that it
159 knows where to send the responses back.</p>
160 <p>There are many publicly usable "anonymous" proxies out there, which
161 provide a further level of indirection between you and the web
163 <p>However, these proxies are called "anonymous" because you don't need
164 to authenticate, not because they would offer any real anonymity. Most
165 of them will log your IP address and make it available to the
166 authorities in case you violate the law of the country they run in. In
167 fact you can't even rule out that some of them only exist to *collect*
168 information on (those suspicious) people with a more than average
169 preference for privacy.</p>
170 <p>If you want to hide your IP address from most adversaries, you
171 should consider chaining <span class="APPLICATION">Privoxy</span> with
172 <a href="https://www.torproject.org/" target="_top">Tor</a>. The
173 configuration details can be found in <a href="#TOR" target="_top">How
174 do I use <span class="APPLICATION">Privoxy</span> together with
175 <span class="APPLICATION">Tor</span> section</a> just below.</p>
178 <h3 class="SECT2"><a name="ANONFORSURE" id="ANONFORSURE">4.8. Can
179 Privoxy guarantee I am anonymous?</a></h3>
180 <p>No. Your chances of remaining anonymous are improved, but unless you
181 <a href="#TOR" target="_top">chain <span class=
182 "APPLICATION">Privoxy</span> with <span class=
183 "APPLICATION">Tor</span></a> or a similar proxy and know what you're
184 doing when it comes to configuring the rest of your system, you should
185 assume that everything you do on the Web can be traced back to you.</p>
186 <p><span class="APPLICATION">Privoxy</span> can remove various
187 information about you, and allows <span class="emphasis"><i class=
188 "EMPHASIS">you</i></span> more freedom to decide which sites you can
189 trust, and what details you want to reveal. But it neither hides your
190 IP address, nor can it guarantee that the rest of the system behaves
191 correctly. There are several possibilities how a web sites can find out
192 who you are, even if you are using a strict <span class=
193 "APPLICATION">Privoxy</span> configuration and chained it with
194 <span class="APPLICATION">Tor</span>.</p>
195 <p>Most of <span class="APPLICATION">Privoxy's</span> privacy-enhancing
196 features can be easily subverted by an insecure browser configuration,
197 therefore you should use a browser that can be configured to only
198 execute code from trusted sites, and be careful which sites you trust.
199 For example there is no point in having <span class=
200 "APPLICATION">Privoxy</span> modify the User-Agent header, if websites
201 can get all the information they want through JavaScript, ActiveX,
203 <p>A few browsers disclose the user's email address in certain
204 situations, such as when transferring a file by FTP. <span class=
205 "APPLICATION">Privoxy</span> does not filter FTP. If you need this
206 feature, or are concerned about the mail handler of your browser
207 disclosing your email address, you might consider products such as
208 <span class="APPLICATION">NSClean</span>.</p>
209 <p>Browsers available only as binaries could use non-standard headers
210 to give out any information they can have access to: see the
211 manufacturer's license agreement. It's impossible to anticipate and
212 prevent every breach of privacy that might occur. The professionally
213 paranoid prefer browsers available as source code, because anticipating
214 their behavior is easier. Trust the source, Luke!</p>
217 <h3 class="SECT2"><a name="PROXYTEST" id="PROXYTEST">4.9. A test site
218 says I am not using a Proxy.</a></h3>
219 <p>Good! Actually, they are probably testing for some other kinds of
220 proxies. Hiding yourself completely would require additional steps.</p>
223 <h3 class="SECT2"><a name="TOR" id="TOR">4.10. How do I use Privoxy
224 together with Tor?</a></h3>
225 <p>Before you configure <span class="APPLICATION">Privoxy</span> to use
226 <a href="https://www.torproject.org/" target="_top">Tor</a>, please
227 follow the <i class="CITETITLE">User Manual</i> chapters <a href=
228 "../user-manual/installation.html" target="_top">2. Installation</a>
229 and <a href="../user-manual/startup.html" target="_top">5. Startup</a>
230 to make sure <span class="APPLICATION">Privoxy</span> itself is setup
232 <p>If it is, refer to <a href=
233 "https://www.torproject.org/documentation.html" target="_top">Tor's
234 extensive documentation</a> to learn how to install <span class=
235 "APPLICATION">Tor</span>, and make sure <span class=
236 "APPLICATION">Tor</span>'s logfile says that <span class="QUOTE">"Tor
237 has successfully opened a circuit"</span> and it <span class=
238 "QUOTE">"looks like client functionality is working"</span>.</p>
239 <p>If either <span class="APPLICATION">Tor</span> or <span class=
240 "APPLICATION">Privoxy</span> isn't working, their combination most
241 likely will neither. Testing them on their own will also help you to
242 direct problem reports to the right audience. If <span class=
243 "APPLICATION">Privoxy</span> isn't working, don't bother the
244 <span class="APPLICATION">Tor</span> developers. If <span class=
245 "APPLICATION">Tor</span> isn't working, don't send bug reports to the
246 <span class="APPLICATION">Privoxy</span> Team.</p>
247 <p>If you verified that <span class="APPLICATION">Privoxy</span> and
248 <span class="APPLICATION">Tor</span> are working, it is time to connect
249 them. As far as <span class="APPLICATION">Privoxy</span> is concerned,
250 <span class="APPLICATION">Tor</span> is just another proxy that can be
251 reached by socks4, socks4a and socks5. Most likely you are interested
252 in <span class="APPLICATION">Tor</span> to increase your anonymity
253 level, therefore you should use socks5, to make sure DNS requests are
254 done through <span class="APPLICATION">Tor</span> and thus invisible to
255 your local network. Using socks4a would work too, but with socks5 you
256 get more precise error messages.</p>
257 <p><span class="APPLICATION">Privoxy's</span> <a href=
258 "../user-manual/config.html" target="_top">main configuration file</a>
259 is already prepared for <span class="APPLICATION">Tor</span>, if you
260 are using a default <span class="APPLICATION">Tor</span> configuration
261 and run it on the same system as <span class=
262 "APPLICATION">Privoxy</span>, you just have to edit the <a href=
263 "../user-manual/config.html#FORWARDING" target="_top">forwarding
264 section</a> and uncomment the line:</p>
265 <table border="0" bgcolor="#E0E0E0" width="100%">
269 # forward-socks5t / 127.0.0.1:9050 .
274 <p>Note that if you got Tor through one of the bundles, you may have to
275 change the port from 9050 to 9150 (or even another one). For details,
276 please check the documentation on the <a href="https://torproject.org/"
277 target="_top">Tor website</a>.</p>
278 <p>This is enough to reach the Internet, but additionally you might
279 want to uncomment the following forward rules, to make sure your local
280 network is still reachable through Privoxy:</p>
281 <table border="0" bgcolor="#E0E0E0" width="100%">
284 <pre class="SCREEN"># forward 192.168.*.*/ .
285 # forward 10.*.*.*/ .
286 # forward 127.*.*.*/ .
291 <p>Unencrypted connections to systems in these address ranges will be
292 as (un)secure as the local network is, but the alternative is that your
293 browser can't reach the network at all. Then again, that may actually
294 be desired and if you don't know for sure that your browser has to be
295 able to reach the local network, there's no reason to allow it.</p>
296 <p>If you want your browser to be able to reach servers in your local
297 network by using their names, you will need additional exceptions that
299 <table border="0" bgcolor="#E0E0E0" width="100%">
302 <pre class="SCREEN"># forward localhost/ .
307 <p>Save the modified configuration file and open <a href=
308 "http://config.privoxy.org/show-status" target=
309 "_top">http://config.privoxy.org/show-status</a> in your browser,
310 confirm that <span class="APPLICATION">Privoxy</span> has reloaded its
311 configuration and that there are no other forward lines, unless you
312 know that you need them. If everything looks good, refer to <a href=
313 "https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#IsMyConnectionPrivate"
314 target="_top">Tor Faq 4.2</a> to learn how to verify that you are
315 really using <span class="APPLICATION">Tor</span>.</p>
316 <p>Afterward, please take the time to at least skim through the rest of
317 <span class="APPLICATION">Tor's</span> documentation. Make sure you
318 understand what <span class="APPLICATION">Tor</span> does, why it is no
319 replacement for application level security, and why you probably don't
320 want to use it for unencrypted logins.</p>
323 <h3 class="SECT2"><a name="SITEBREAK" id="SITEBREAK">4.11. Might some
324 things break because header information or content is being
326 <p>Definitely. It is common for sites to use browser type, browser
327 version, HTTP header content, and various other techniques in order to
328 dynamically decide what to display and how to display it. What you see,
329 and what I see, might be very different. There are many, many ways that
330 this can be handled, so having hard and fast rules, is tricky.</p>
331 <p>The <span class="QUOTE">"User-Agent"</span> is sometimes used in
332 this way to identify the browser, and adjust content accordingly.</p>
333 <p>Also, different browsers use different encodings of non-English
334 characters, certain web servers convert pages on-the-fly according to
335 the User Agent header. Giving a <span class="QUOTE">"User Agent"</span>
336 with the wrong operating system or browser manufacturer causes some
337 sites in these languages to be garbled; Surfers to Eastern European
338 sites should change it to something closer. And then some page access
339 counters work by looking at the <span class="QUOTE">"Referer"</span>
340 header; they may fail or break if unavailable. The weather maps of
341 Intellicast have been blocked by their server when no <span class=
342 "QUOTE">"Referer"</span> or cookie is provided, is another example.
343 (But you can forge both headers without giving information away). There
344 are many other ways things can go wrong when trying to fool a web
345 server. The results of which could inadvertently cause pages to load
346 incorrectly, partially, or even not at all. And there may be no obvious
347 clues as to just what went wrong, or why. Nowhere will there be a
348 message that says <span class="QUOTE">"<span class="emphasis"><i class=
349 "EMPHASIS">Turn off <tt class="LITERAL">fast-redirects</tt> or
350 else!</i></span> "</span></p>
351 <p>Similar thoughts apply to modifying JavaScript, and, to a lesser
352 degree, HTML elements.</p>
353 <p>If you have problems with a site, you will have to adjust your
354 configuration accordingly. Cookies are probably the most likely
355 adjustment that may be required, but by no means the only one.</p>
358 <h3 class="SECT2"><a name="CACHING" id="CACHING">4.12. Can Privoxy act
359 as a <span class="QUOTE">"caching"</span> proxy to speed up web
361 <p>No, it does not have this ability at all. You want something like
362 <a href="http://www.squid-cache.org/" target="_top">Squid</a> or
363 <a href="http://www.pps.jussieu.fr/~jch/software/polipo/" target=
364 "_top">Polipo</a> for this. And, yes, before you ask, <span class=
365 "APPLICATION">Privoxy</span> can co-exist with other kinds of proxies
366 like <span class="APPLICATION">Squid</span>. See the <a href=
367 "../user-manual/config.html#FORWARDING" target="_top">forwarding
368 chapter</a> in the <a href="../user-manual/index.html" target=
369 "_top">user manual</a> for details.</p>
372 <h3 class="SECT2"><a name="FIREWALL" id="FIREWALL">4.13. What about as
373 a firewall? Can Privoxy protect me?</a></h3>
374 <p>Not in the way you mean, or in the way some firewall vendors claim
375 they can. <span class="APPLICATION">Privoxy</span> can help protect
376 your privacy, but can't protect your system from intrusion attempts. It
377 is, of course, perfectly possible to use <span class=
378 "emphasis"><i class="EMPHASIS">both</i></span>.</p>
381 <h3 class="SECT2"><a name="WASTED" id="WASTED">4.14. I have large empty
382 spaces / a checkerboard pattern now where ads used to be. Why?</a></h3>
383 <p>It is technically possible to eliminate banners and ads in a way
384 that frees their allocated page space. This could easily be done by
385 blocking with <span class="APPLICATION">Privoxy's</span> filters, and
386 eliminating the <span class="emphasis"><i class=
387 "EMPHASIS">entire</i></span> image references from the HTML page
389 <p>But, this would consume considerably more CPU resources (IOW, slow
390 things down), would likely destroy the layout of some web pages which
391 rely on the banners utilizing a certain amount of page space, and might
392 fail in other cases, where the screen space is reserved (e.g. by HTML
393 tables for instance). Also, making ads and banners disappear without
394 any trace complicates troubleshooting, and would sooner or later be
396 <p>The better alternative is to instead let them stay, and block the
397 resulting requests for the banners themselves as is now the case. This
398 leaves either empty space, or the familiar checkerboard pattern.</p>
399 <p>So the developers won't support this in the default configuration,
400 but you can of course define appropriate filters yourself to achieve
404 <h3 class="SECT2"><a name="SSL" id="SSL">4.15. How can Privoxy filter
405 Secure (HTTPS) URLs?</a></h3>
406 <p>Since secure HTTP connections are encrypted SSL sessions between
407 your browser and the secure site, and are meant to be reliably
408 <span class="emphasis"><i class="EMPHASIS">secure</i></span>, there is
409 little that <span class="APPLICATION">Privoxy</span> can do but hand
410 the raw gibberish data though from one end to the other
412 <p>The only exception to this is blocking by host patterns, as the
413 client needs to tell <span class="APPLICATION">Privoxy</span> the name
414 of the remote server, so that <span class="APPLICATION">Privoxy</span>
415 can establish the connection. If that name matches a host-only pattern,
416 the connection will be blocked.</p>
417 <p>As far as ad blocking is concerned, this is less of a restriction
418 than it may seem, since ad sources are often identifiable by the host
419 name, and often the banners to be placed in an encrypted page come
420 unencrypted nonetheless for efficiency reasons, which exposes them to
421 the full power of <span class="APPLICATION">Privoxy</span>'s ad
423 <p><span class="QUOTE">"Content cookies"</span> (those that are
424 embedded in the actual HTML or JS page content, see <tt class=
426 "../user-manual/actions-file.html#FILTER-CONTENT-COOKIES" target=
427 "_top">filter{content-cookies}</a></tt>), in an SSL transaction will be
428 impossible to block under these conditions. Fortunately, this does not
429 seem to be a very common scenario since most cookies come by
430 traditional means.</p>
433 <h3 class="SECT2"><a name="SECURE" id="SECURE">4.16. Privoxy runs as a
434 <span class="QUOTE">"server"</span>. How secure is it? Do I need to
435 take any special precautions?</a></h3>
436 <p>On Unix-like systems, <span class="APPLICATION">Privoxy</span> can
437 run as a non-privileged user, which is how we recommend it be run.
438 Also, by default <span class="APPLICATION">Privoxy</span> listens to
439 requests from <span class="QUOTE">"localhost"</span> only.</p>
440 <p>The server aspect of <span class="APPLICATION">Privoxy</span> is not
441 itself directly exposed to the Internet in this configuration. If you
442 want to have <span class="APPLICATION">Privoxy</span> serve as a LAN
443 proxy, this will have to be opened up to allow for LAN requests. In
444 this case, we'd recommend you specify only the LAN gateway address,
445 e.g. 192.168.1.1, in the main <span class="APPLICATION">Privoxy</span>
446 configuration file and check all <a href=
447 "../user-manual/config.html#ACCESS-CONTROL" target="_top">access
448 control and security options</a>. All LAN hosts can then use this as
449 their proxy address in the browser proxy configuration, but
450 <span class="APPLICATION">Privoxy</span> will not listen on any
451 external interfaces. ACLs can be defined in addition, and using a
452 firewall is always good too. Better safe than sorry.</p>
455 <h3 class="SECT2"><a name="TURNOFF" id="TURNOFF">4.17. Can I
456 temporarily disable Privoxy?</a></h3>
457 <p><span class="APPLICATION">Privoxy</span> doesn't have a transparent
458 proxy mode, but you can toggle off blocking and content filtering.</p>
459 <p>The easiest way to do that is to point your browser to the remote
460 toggle URL: <a href="http://config.privoxy.org/toggle" target=
461 "_top">http://config.privoxy.org/toggle</a>.</p>
462 <p>See the <a href="../user-manual/appendix.html#BOOKMARKLETS" target=
463 "_top">Bookmarklets section</a> of the <i class="CITETITLE">User
464 Manual</i> for an easy way to access this feature. Note that this is a
465 feature that may need to be enabled in the main <tt class=
466 "FILENAME">config</tt> file.</p>
469 <h3 class="SECT2"><a name="REALLYOFF" id="REALLYOFF">4.18. When
470 <span class="QUOTE">"disabled"</span> is Privoxy totally out of the
472 <p>No, this just means all optional filtering and actions are disabled.
473 <span class="APPLICATION">Privoxy</span> is still acting as a proxy,
474 but just doing less of the things that <span class=
475 "APPLICATION">Privoxy</span> would normally be expected to do. It is
476 still a <span class="QUOTE">"middle-man"</span> in the interaction
477 between your browser and web sites. See below to bypass the proxy.</p>
480 <h3 class="SECT2"><a name="TURNOFF2" id="TURNOFF2">4.19. How can I tell
481 Privoxy to totally ignore certain sites?</a></h3>
482 <p>Bypassing a proxy, or proxying based on arbitrary criteria, is
483 purely a browser configuration issue, not a <span class=
484 "APPLICATION">Privoxy</span> issue. Modern browsers typically do have
485 settings for not proxying certain sites. Check your browser's help
489 <h3 class="SECT2"><a name="CRUNCH" id="CRUNCH">4.20. My logs show
490 Privoxy <span class="QUOTE">"crunches"</span> ads, but also its own
491 internal CGI pages. What is a <span class=
492 "QUOTE">"crunch"</span>?</a></h3>
493 <p>A <span class="QUOTE">"crunch"</span> means <span class=
494 "APPLICATION">Privoxy</span> intercepted <span class=
495 "emphasis"><i class="EMPHASIS">something</i></span>, nothing more.
496 Often this is indeed ads or banners, but <span class=
497 "APPLICATION">Privoxy</span> uses the same mechanism for trapping
498 requests for its own internal pages. For instance, a request for
499 <span class="APPLICATION">Privoxy's</span> configuration page at:
500 <a href="http://config.privoxy.org" target=
501 "_top">http://config.privoxy.org</a>, is intercepted (i.e. it does not
502 go out to the 'net), and the familiar CGI configuration is returned to
503 the browser, and the log consequently will show a <span class=
504 "QUOTE">"crunch"</span>.</p>
505 <p>Since version 3.0.7, Privoxy will also log the crunch reason. If you
506 are using an older version you might want to upgrade.</p>
509 <h3 class="SECT2"><a name="DOWNLOADS" id="DOWNLOADS">4.21. Can Privoxy
510 affect files that I download from a webserver? FTP server?</a></h3>
511 <p>From the webserver's perspective, there is no difference between
512 viewing a document (i.e. a page), and downloading a file. The same is
513 true of <span class="APPLICATION">Privoxy</span>. If there is a match
514 for a <tt class="LITERAL"><a href=
515 "../user-manual/actions-file.html#BLOCK" target="_top">block</a></tt>
516 pattern, it will still be blocked, and of course this is obvious.</p>
517 <p>Filtering is potentially more of a concern since the results are not
518 always so obvious, and the effects of filtering are there whether the
519 file is simply viewed, or downloaded. And potentially whether the
520 content is some obnoxious advertisement, or Mr. Jimmy's latest/greatest
521 source code jewel. Of course, one of these presumably is <span class=
522 "QUOTE">"bad"</span> content that we don't want, and the other is
523 <span class="QUOTE">"good"</span> content that we do want. <span class=
524 "APPLICATION">Privoxy</span> is blind to the differences, and can only
525 distinguish <span class="QUOTE">"good from bad"</span> by the
526 configuration parameters <span class="emphasis"><i class=
527 "EMPHASIS">we</i></span> give it.</p>
528 <p><span class="APPLICATION">Privoxy</span> knows the differences in
529 files according to the <span class="QUOTE">"Content Type"</span> as
530 reported by the webserver. If this is reported accurately (e.g.
531 <span class="QUOTE">"application/zip"</span> for a zip archive), then
532 <span class="APPLICATION">Privoxy</span> knows to ignore these where
533 appropriate. <span class="APPLICATION">Privoxy</span> potentially can
534 filter HTML as well as plain text documents, subject to configuration
535 parameters of course. Also, documents that are of an unknown type
536 (generally assumed to be <span class="QUOTE">"text/plain"</span>) can
537 be filtered, as will those that might be incorrectly reported by the
538 webserver. If such a file is a downloaded file that is intended to be
539 saved to disk, then any content that might have been altered by
540 filtering, will be saved too, for these (probably rare) cases.</p>
541 <p>Note that versions later than 3.0.2 do NOT filter document types
542 reported as <span class="QUOTE">"text/plain"</span>. Prior to this,
543 <span class="APPLICATION">Privoxy</span> did filter this document
545 <p>In short, filtering is <span class="QUOTE">"ON"</span> if a) the
546 content type as reported by the webserver is appropriate <span class=
547 "emphasis"><i class="EMPHASIS">and</i></span> b) the configuration
548 allows it (or at least does not disallow it). That's it. There is no
549 magic cookie anywhere to say this is <span class="QUOTE">"good"</span>
550 and this is <span class="QUOTE">"bad"</span>. It's the configuration
551 that lets it all happen or not.</p>
552 <p>If you download text files, you probably do not want these to be
553 filtered, particularly if the content is source code, or other critical
554 content. Source code sometimes might be mistaken for Javascript (i.e.
555 the kind that might open a pop-up window). It is recommended to turn
556 off filtering for download sites (particularly if the content may be
557 plain text files and you are using version 3.0.2 or earlier) in your
558 <tt class="FILENAME">user.action</tt> file. And also, for any site or
559 page where making <span class="emphasis"><i class=
560 "EMPHASIS">any</i></span> changes at all to the content is to be
562 <p><span class="APPLICATION">Privoxy</span> does not do FTP at all,
563 only HTTP and HTTPS (SSL) protocols.</p>
566 <h3 class="SECT2"><a name="DOWNLOADS2" id="DOWNLOADS2">4.22. I just
567 downloaded a Perl script, and Privoxy altered it! Yikes, what is
569 <p>Please read above.</p>
572 <h3 class="SECT2"><a name="HOSTSFILE" id="HOSTSFILE">4.23. Should I
573 continue to use a <span class="QUOTE">"HOSTS"</span> file for
574 ad-blocking?</a></h3>
575 <p>One time-tested technique to defeat common ads is to trick the local
576 DNS system by giving a phony IP address for the ad generator in the
577 local <tt class="FILENAME">HOSTS</tt> file, typically using <tt class=
578 "LITERAL">127.0.0.1</tt>, aka <tt class="LITERAL">localhost</tt>. This
579 effectively blocks the ad.</p>
580 <p>There is no reason to use this technique in conjunction with
581 <span class="APPLICATION">Privoxy</span>. <span class=
582 "APPLICATION">Privoxy</span> does essentially the same thing, much more
583 elegantly and with much more flexibility. A large <tt class=
584 "FILENAME">HOSTS</tt> file, in fact, not only duplicates effort, but
585 may get in the way and seriously slow down your system. It is
586 recommended to remove such entries from your <tt class=
587 "FILENAME">HOSTS</tt> file. If you think your hosts list is neglected
588 by <span class="APPLICATION">Privoxy's</span> configuration, consider
589 adding your list to your <tt class="FILENAME">user.action</tt>
591 <table border="0" bgcolor="#E0E0E0" width="100%">
594 <pre class="SCREEN"> { +block }
597 ads.galore.example.com
598 etc.example.com</pre>
604 <h3 class="SECT2"><a name="SEEALSO" id="SEEALSO">4.24. Where can I find
605 more information about Privoxy and related issues?</a></h3>
606 <p>Other references and sites of interest to <span class=
607 "APPLICATION">Privoxy</span> users:</p>
611 <td><a href="https://www.privoxy.org/" target=
612 "_top">https://www.privoxy.org/</a>, the <span class=
613 "APPLICATION">Privoxy</span> Home page.</td>
620 <td><a href="https://www.privoxy.org/faq/" target=
621 "_top">https://www.privoxy.org/faq/</a>, the <span class=
622 "APPLICATION">Privoxy</span> FAQ.</td>
629 <td><a href="https://www.privoxy.org/developer-manual/" target=
630 "_top">https://www.privoxy.org/developer-manual/</a>, the
631 <span class="APPLICATION">Privoxy</span> developer manual.</td>
638 <td><a href="https://sourceforge.net/projects/ijbswa/" target=
639 "_top">https://sourceforge.net/projects/ijbswa/</a>, the Project
640 Page for <span class="APPLICATION">Privoxy</span> on <a href=
641 "http://sourceforge.net" target="_top">SourceForge</a>.</td>
648 <td><a href="http://config.privoxy.org/" target=
649 "_top">http://config.privoxy.org/</a>, the web-based user
650 interface. <span class="APPLICATION">Privoxy</span> must be
651 running for this to work. Shortcut: <a href="http://p.p/" target=
652 "_top">http://p.p/</a></td>
660 "https://sourceforge.net/tracker/?group_id=11118&atid=460288"
662 "_top">https://sourceforge.net/tracker/?group_id=11118&atid=460288</a>,
663 to submit <span class="QUOTE">"misses"</span> and other
664 configuration related suggestions to the developers.</td>
671 <td><a href="http://www.squid-cache.org/" target=
672 "_top">http://www.squid-cache.org/</a>, a popular caching proxy,
673 which is often used together with <span class=
674 "APPLICATION">Privoxy</span>.</td>
682 "http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/"
684 "_top">http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/</a>,
685 <span class="APPLICATION">Polipo</span> is a caching proxy with
686 advanced features like pipelining, multiplexing and caching of
687 partial instances. In many setups it can be used as <span class=
688 "APPLICATION">Squid</span> replacement.</td>
695 <td><a href="https://www.torproject.org/" target=
696 "_top">https://www.torproject.org/</a>, <span class=
697 "APPLICATION">Tor</span> can help anonymize web browsing, web
698 publishing, instant messaging, IRC, SSH, and other
705 <h3 class="SECT2"><a name="MICROSUCK" id="MICROSUCK">4.25. I've noticed
706 that Privoxy changes <span class="QUOTE">"Microsoft"</span> to
707 <span class="QUOTE">"MicroSuck"</span>! Why are you manipulating my
709 <p>We're not. The text substitutions that you are seeing are disabled
710 in the default configuration as shipped. You have either manually
711 activated the <span class="QUOTE">"<tt class="LITERAL">fun</tt>"</span>
712 filter which is clearly labeled <span class="QUOTE">"Text replacements
713 for subversive browsing fun!"</span> or you are using an older Privoxy
714 version and have implicitly activated it by choosing the <span class=
715 "QUOTE">"Advanced"</span> profile in the web-based editor. Please
719 <h3 class="SECT2"><a name="VALID" id="VALID">4.26. Does Privoxy produce
720 <span class="QUOTE">"valid"</span> HTML (or XHTML)?</a></h3>
721 <p>Privoxy generates HTML in both its own <span class=
722 "QUOTE">"templates"</span>, and possibly whenever there are text
723 substitutions via a <span class="APPLICATION">Privoxy</span> filter.
724 While this should always conform to the HTML 4.01 specifications, it
725 has not been validated against this or any other standard.</p>
728 <h3 class="SECT2"><a name="SURPRISE-PRIVOXY" id=
729 "SURPRISE-PRIVOXY">4.27. How did you manage to get Privoxy on my
730 computer without my consent?</a></h3>
731 <p>We didn't. We make Privoxy available for download, but we don't go
732 around installing it on other people's systems behind their back. If
733 you discover Privoxy running on your system and are sure you didn't
734 install it yourself, somebody else did. You may not even be running the
735 real Privoxy, but maybe something else that only pretends to be
736 Privoxy, or maybe something that is based on the real Privoxy, but has
738 <p>Lately there have been reports of problems with some kind of
739 "parental control" software based on Privoxy that came preinstalled on
740 certain <a href="https://sourceforge.net/p/ijbswa/bugs/813/" target=
741 "_top">ASUS Netbooks</a>. The problems described are inconsistent with
742 the behaviour of official Privoxy versions, which suggests that the
743 preinstalled software may contain vendor modifications that we don't
744 know about and thus can't debug.</p>
745 <p>Privoxy's <a href="copyright.html">license</a> allows vendor
746 modifications, but the vendor has to comply with the license, which
747 involves informing the user about the changes and to make the changes
748 available under the same license as Privoxy itself.</p>
749 <p>If you are having trouble with a modified Privoxy version, please
750 try to talk to whoever made the modifications before reporting the
751 problem to us. Please also try to convince whoever made the
752 modifications to talk to us. If you think somebody gave you a modified
753 Privoxy version without complying to the license, please let us
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