May 18, 2009

ethernet-cableby Carl Anctil

I have been using Privoxy for many, many years. It was actually called the Internet Junkbuster when I was first introduced to it. In early 2000 when I started getting into security and privacy, it was one of the first tools I began using to disguise my user-agent string.

Modifying a user-agent string is a simple way to avoid malware infections from websites that use the user-agent string as a method to determine the browser type and version in order to infect or hijack a browser (most common with IE). I modify the user-agent string to this day. However, what I do now is pretty subtle. I add or remove a single dot somewhere within the string. This way, if someone quickly glances at logs, my new customized user-agent string doesn’t stick out like a sore thumb.

Another reason I like using Privoxy is to block banner adds. Especially today, with all the XSS vulnerabilities going around, this is quick and simple way to eliminate this threat. I also believe in cookie management. Privoxy can be used to manage your browser cookies and how they interact with websites. You can block them altogether or modify them to force a particular behavior, such as whether they are session cookies or permanent cookies. I know this is possible from within the browser, but Privoxy offers many more options and more flexibility for cookie management. It’s really cool stuff once you get into cookies and the how and why they work.

Privoxy is an effective tool for controlling tracking web bugs. Web bugs are tiny 1×1 images used to report back to a company (website) whether you have opened or visited a certain page. Once this 1×1 image is rendered by the browser, various statistics are sent back to the requesting server such as the IP address, date and time, browser version and type, etc. This information is usually sent directly to a third party which usually is an advertising company. But there are other uses for this technology such as by some services that will advise you when an email (including webmail) has been read.

Lastly, I like Privoxy because I can also control the referrer. When a connection is made to a website, the browser will let the web server know which URL it came from. This is called the referrer. With Privoxy it’s possible to modify or block the referrer string that is sent to a web server when a new connection is made. This way web servers think you browsed directly to the url instead of having clicked from a link (being referred by).

Privoxy is a proxy. It runs in the background. I install it locally on every computer I have. I have it run locally on the loopback interface, which is the default. The browser will need to be configured to use the local proxy for it to perform the necessary scrubbing. For myself, Privoxy is simply another tool or software like antivirus, antispyware, etc. It doesn’t matter whether I’m on Windows, Mac or Linux, I install and use Privoxy when possible.

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