Privoxy Frequently Asked Questions
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# 1. General Information

### 1.1. Who should give Privoxy a try?

Anyone who is interested in security, privacy, or in finer-grained control over their web and Internet experience.

### 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 with the willingness to read the documentation and the ability to fine-tune their installation will benefit the most.

One of Privoxy's strengths 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, 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. Also note that the web-based action editor doesn't use authentication and should only be enabled in environments where all clients with access to Privoxy listening port can be trusted.

### 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 to web servers directly. The clients then ask the proxy to request objects (web pages, images, movies etc) on their behalf and to forward the data to the clients. It is a "go-between". For details, see Wikipedia's proxy definition.

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 enhancement, 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. The new Privoxy still blocks ads and banners, still manages cookies, and still helps protect your privacy. But, most of these features have been enhanced, and many new ones have been added, all in the same vein.

Privoxy's new features include:

- Supports "Connection: keep-alive". Outgoing connections can be kept alive independently from the client.

- Supports IPv6, provided the operating system does so too, and the configure script detects it.

- Supports tagging which allows to change the behaviour based on client and server headers.

- Can be run as an "intercepting" proxy, which obviates the need to configure browsers individually.

- Sophisticated actions and filters for manipulating both server and client headers.

- Can be chained with other proxies.

- 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" and HTML annoyances, 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.

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

- GIF de-animation.

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

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

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

- Most features are controllable on a per-site or per-location basis.

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

### 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?

That depends on your expectations. The default installation should give you a good starting point, and block most ads and unwanted content, but many of the more advanced features are off by default, and 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 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 very versatile and powerful, and can probably do a number of things your browser 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.

Note, however, that it's recommended to leverage both your browser's and Privoxy's privacy enhancing features at the same time. While your browser probably lacks some features Privoxy offers, it should also be able to do some things more reliable, for example restricting and suppressing JavaScript.

### 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 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 free software and licensed under the GNU General Public License (GPL) version 2. 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.

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

No, at least not reliably enough to trust it. Privoxy is not designed to be a malware removal tool and the default configuration doesn't even try to filter out any malware.

Privoxy could help prevent contact from (known) sites that use such tactics with appropriate configuration rules, and thus could conceivably prevent contamination from such sites. However, keeping such a configuration up to date would require a lot of time and effort that would be better spend on keeping your software itself up to date so it doesn't have known vulnerabilities.

### 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 might be better to choose one software or the other and work a little to tweak its configuration to your liking.

Note that this is an advice specific to ad blocking.

### 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 or responding to user questions on the mailing lists.

So first thing, subscribe to the Privoxy Users or the Privoxy Developers mailing list, join the discussion, help out other users, provide general feedback or report problems you noticed.

If you intend to help out with the trackers, you also might want to get an account on SourceForge.net so we don't confuse you with the other name-less users.

We also have a Developer's Manual. While it is partly out of date, it's still worth reading.

Our TODO list may be of interest to you as well. Please let us know if you want to work on one of the items listed.

#### 1.17.2. Would you like to donate?

Privoxy is developed by unpaid volunteers and thus our current running costs are pretty low. Nevertheless, we have plans that will cost money in the future. We would like to get this money through donations made by our users.

Privoxy has therefore become an associated project of Software in the Public Interest (SPI), which allows us to receive tax-deductible donations in most western countries.

We intend to use the donations to pay for our domain after transfering it to SPI. Our goal is to make sure there's no single point of failure and the bill gets paid and the site keeps running even if a some of the currently active developers were to suddenly disappear for a while.

We would also like to spend some money on more reliable hosting, on hardware to help make sure Privoxy keeps running on platforms the developers currently can't test on, and on technical books to educate our developers about said platforms or to improve their knowledge in general.

If you enjoy our software and feel like helping out with a donation, please have a look at SPI's donation page to see what the options are.

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