Privoxy Frequently Asked Questions
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# 1. General Information

### 1.1. What is this new version of Privoxy?

In the beginning, there was the Internet Junkbuster, by Anonymous Coders and Junkbusters Corporation. It 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 users to consume ads, give up autonomy over their browsing, and for spying on them, kept 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.

### 1.2. Why "Privoxy"? Why a name change at all?

Privoxy is the "Privacy Enhancing Proxy". Also, its content modification and junk suppression allow you to browse your "private edition" of the web.

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 the continued 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 changes from the original code, that it was time to make a clean break from the past and make a name in their own right.

### 1.3. 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 enhanced, and 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 note to upgraders for details.

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 content filtering (removes banners based on size, invisible "web-bugs", JavaScript and HTML annoyances, pop-up windows, 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.

### 1.4. 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 the 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.

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

Privoxy is a proxy that is solely focused on privacy protection and junk elimination. 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 control via the various configuration files and options.

### 1.5. 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 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 configurable.

### 1.6. 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.)

### 1.7. 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 unwanted content.

But 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!

### 1.8. 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. This way all the configuration is in one place, and you don't have to maintain a similar configuration for possibly many browsers.

### 1.9. 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!

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

#### 1.10.1. Money Money Money

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.

#### 1.10.2. 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.

#### 1.10.3. You want to work with us?

Well, helping the team is always a good idea. We welcome new developers, packaging gurus or documentation writers. Simply get an account on SourceForge.net and mail your id to the developers mailing list. Then read the Developer's Manual.

Once we have added you to the team, you'll have write access to the CVS repository, and together we'll find a suitable task for you.

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