Privoxy Frequently Asked Questions
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# 1. General Information

### 1.1. Who should use Privoxy?

Anyone that is interested in security, privacy, or in finer-grained control over their web and Internet experience. Everyone is encouraged to try Privoxy.

### 1.2. Is Privoxy the best choice for me?

Privoxy is certainly a good choice, especially for those who want more control and security. Those that have the ability to fine-tune their installation will benefit the most. One of Privoxy's strength's is that it is highly configurable giving you the ability to completely personalize your installation. Being familiar with, or at least having an interest in learning about HTTP and other networking protocols, HTML, IP (Internet Protocol), and "Regular Expressions" will be a big plus and will help you get the most out of Privoxy. A new installation just includes a very basic configuration. The user should take this as a starting point only, and enhance it as he or she sees fit. In fact, the user is encouraged, and expected to, fine-tune the configuration.

Much of Privoxy's configuration can be done with a Web browser. But there are areas where configuration is done using a text editor to edit configuration files.

### 1.3. What is a "proxy"? How does Privoxy work?

A web proxy is a service, based on a software such as Privoxy, that clients (i.e. browsers) can use instead of connecting directly to web servers on the Internet. The clients then ask the proxy to fetch the objects they need (web pages, images, movies etc) on their behalf, and when the proxy has done so, it hands the results back to the client. It is a "go-between". See the Wikipedia proxy definition for more.

There are many reasons to use web proxies, such as security (firewalling), efficiency (caching) and others, and there are any number of proxies to accommodate those needs.

Privoxy is a proxy that is primarily focused on privacy protection, ad and junk elimination and freeing the user from restrictions placed on his activities. Sitting between your browser(s) and the Internet, it is in a perfect position to filter outbound personal information that your browser is leaking, as well as inbound junk. It uses a variety of techniques to do this, all of which are under your complete control via the various configuration files and options. Being a proxy also makes it easier to share configurations among multiple browsers and/or users.

### 1.4. Does Privoxy do anything more than ad blocking?

Yes, ad blocking is but one possible use. There are many, many ways Privoxy can be used to sanitize and customize web browsing.

### 1.5. What is this new version of "Junkbuster"?

A long time ago, there was the Internet Junkbuster, by Anonymous Coders and Junkbusters Corporation. This saved many users a lot of pain in the early days of web advertising and user tracking.

But the web, its protocols and standards, and with it, the techniques for forcing ads on users, give up autonomy over their browsing, and for tracking them, keeps evolving. Unfortunately, the Internet Junkbuster did not. Version 2.0.2, published in 1998, was (and is) the last official release available from Junkbusters Corporation. Fortunately, it had been released under the GNU GPL, which allowed further development by others.

So Stefan Waldherr started maintaining an improved version of the software, to which eventually a number of people contributed patches. It could already replace banners with a transparent image, and had a first version of pop-up killing, but it was still very closely based on the original, with all its limitations, such as the lack of HTTP/1.1 support, flexible per-site configuration, or content modification. The last release from this effort was version 2.0.2-10, published in 2000.

Then, some developers picked up the thread, and started turning the software inside out, upside down, and then reassembled it, adding many new features along the way.

The result of this is Privoxy, whose first stable version, 3.0, was released August, 2002.

### 1.6. Why "Privoxy"? Why change the name from Junkbuster at all?

Though outdated, Junkbusters Corporation continues to offer their original version of the Internet Junkbuster, so publishing our Junkbuster-derived software under the same name led to confusion.

There are also potential legal complications from our use of the Junkbuster name, which is a registered trademark of Junkbusters Corporation. There are, however, no objections from Junkbusters Corporation to the Privoxy project itself, and they, in fact, still share our ideals and goals.

The developers also believed that there are so many improvements over the original code, that it was time to make a clean break from the past and make a name in their own right.

Privoxy is the "Privacy Enhancing Proxy". Also, its content modification and junk suppression gives you, the user, more control, more freedom, and allows you to browse your personal and "private edition" of the web.

### 1.7. How does Privoxy differ from the old Junkbuster?

Privoxy picks up where Junkbuster left off. All the old features remain. The new Privoxy still blocks ads and banners, still manages cookies, and still helps protect your privacy. But, these are all greatly enhanced, and many, many new features have been added, all in the same vein.

The configuration has changed significantly as well. This is something that users will notice right off the bat if upgrading from Junkbuster 2.0.x. The "blocklist" "cookielist", "imagelist" and much more has been combined into the "actions" files, with a completely different syntax. See the What's New page for the latest updates.

Privoxy's new features include:

- Integrated browser based configuration and control utility at http://config.privoxy.org/ (shortcut: http://p.p/). Browser-based tracing of rule and filter effects. Remote toggling.

- Web page filtering (text replacements, removes banners based on size, invisible "web-bugs", JavaScript and HTML annoyances, pop-up windows, header manipulation, etc.)

- Modularized configuration that allows for standard settings and user settings to reside in separate files, so that installing updated actions files won't overwrite individual user settings.

- HTTP/1.1 compliant (but not all optional 1.1 features are supported).

- Support for Perl Compatible Regular Expressions in the configuration files, and generally a more sophisticated and flexible configuration syntax over previous versions.

- Improved cookie management features (e.g. session based cookies).

- GIF de-animation.

- Bypass many click-tracking scripts (avoids script redirection).

- Multi-threaded (POSIX and native threads).

- User-customizable HTML templates for all proxy-generated pages (e.g. "blocked" page).

- Auto-detection and re-reading of config file changes.

- Improved signal handling, and a true daemon mode (Unix).

- Every feature now controllable on a per-site or per-location basis, configuration more powerful and versatile over-all.

- Many smaller new features added, limitations and bugs removed, and security holes fixed.

### 1.8. How does Privoxy know what is an ad, and what is not?

Privoxy's approach to blocking ads is twofold:

First, there are certain patterns in the locations (URLs) of banner images. This applies to both the path (you wouldn't guess how many web sites serve their banners from a directory called "banners"!) and the host (blocking the big banner hosting services like doublecklick.net already helps a lot). Privoxy takes advantage of this fact by using URL patterns to sort out and block the requests for things that sound like they would be ads or banners.

Second, banners tend to come in certain sizes. But you can't tell the size of an image by its URL without downloading it, and if you do, it's too late to save bandwidth. Therefore, Privoxy also inspects the HTML sources of web pages while they are loaded, and replaces references to images with standard banner sizes by dummy references, so that your browser doesn't request them anymore in the first place.

Both of this involves a certain amount of guesswork and is, of course, freely and readily configurable.

### 1.9. Can Privoxy make mistakes? This does not sound very scientific.

Actually, it's a black art ;-) And yes, it is always possible to have a broad rule accidentally block or change something by mistake. You will almost surely run into such situations at some point. It is tricky writing rules to cover every conceivable possibility, and not occasionally get false positives.

But this should not be a big concern since the Privoxy configuration is very flexible, and includes tools to help identify these types of situations so they can be addressed as needed, allowing you to customize your installation. (See the Troubleshooting section below.)

### 1.10. Will I have to configure Privoxy before I can use it?

No, not really. The default installation should give you a good starting point, and block most ads and unwanted content. Many of the more advanced features are off by default, and would require you to activate them.

You do have to set up your browser to use Privoxy (see the Installation section below).

And you will certainly run into situations where there are false positives, or ads not being blocked that you may not want to see. In these cases, you would certainly benefit by customizing Privoxy's configuration to more closely match your individual situation. And we would encourage you to do this. This is where the real power of Privoxy lies!

### 1.11. Can Privoxy run as a server on a network?

Yes, Privoxy runs as a server already, and can easily be configured to "serve" more than one client. See How can I set up Privoxy to act as a proxy for my LAN below.

### 1.12. My browser does the same things as Privoxy. Why should I use Privoxy at all?

Modern browsers do indeed have some of the same functionality as Privoxy. Maybe this is adequate for you. But Privoxy is much more versatile and powerful, and can do a number of things that browsers just can't.

In addition, a proxy is good choice if you use multiple browsers, or have a LAN with multiple computers since Privoxy can run as a server application. This way all the configuration is in one place, and you don't have to maintain a similar configuration for possibly many browsers or users.

### 1.13. Why should I trust Privoxy?

The most important reason is because you have access to everything, and you can control everything. You can check every line of every configuration file yourself. You can check every last bit of source code should you desire. And even if you can't read code, there should be some comfort in knowing that thousands of other people can, and do read it. You can build the software from scratch, if you want, so that you know the executable is clean, and that it is yours. In fact, we encourage this level of scrutiny. It is one reason we use Privoxy ourselves.

### 1.14. Is there is a license or fee? What about a warranty? Registration?

Privoxy is licensed under the GNU General Public License (GPL). It is free to use, copy, modify or distribute as you wish under the terms of this license. Please see the Copyright section for more information on the license and copyright. Or the `LICENSE` file that should be included.

There is no warranty of any kind, expressed, implied or otherwise. That is something that would cost real money ;-) There is no registration either. Privoxy really is free in every respect!

### 1.15. Can Privoxy remove spyware? Adware? Viruses?

No. Privoxy cannot remove anything. It is not a removal tool. It is a preventative. Privoxy can help prevent contact from sites that use such tactics with appropriate configuration rules, and thus could conceivably prevent contamination from such sites.

### 1.16. Can I use Privoxy with other ad-blocking software?

Privoxy should work fine with other proxies and other software in general.

But it is probably not necessary to use Privoxy in conjunction with other ad-blocking products, and this could conceivably cause undesirable results. It would be better to choose one software or the other and work a little to tweak its configuration to your liking.

### 1.17. I would like to help you, what can I do?

#### 1.17.1. Would you like to participate?

Well, we always need help. There is something for everybody who wants to help us. We welcome new developers, packagers, testers, documentation writers or really anyone with a desire to help in any way. You DO NOT need to be a "programmer". There are many other tasks available. In fact, the programmers often can't spend as much time programming because of some of the other, more mundane things that need to be done, like checking the Tracker feedback sections.

So first thing, get an account on SourceForge.net and mail your id to the developers mailing list. Then, please read the Developer's Manual, at least the pertinent sections.

#### 1.17.2. Contribute!

We, of course, welcome donations and could use money for domain registering, buying software to test Privoxy with, and, of course, for regular world-wide get-togethers (hahaha). If you enjoy the software and feel like helping us with a donation, just drop us a note.

#### 1.17.3. Software

If you are a vendor of a web-related software like a browser, web server or proxy, and would like us to ensure that Privoxy runs smoothly with your product, you might consider supplying us with a copy or license. We can't, however, guarantee that we will fix all potential compatibility issues as a result.

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