The Electronic Frontier Foundation has published an interesting theory that it is possible to track web browsers based on their web browser’s fingerprint. This fingerprint is of course the data that can be accessed by the server or website the browser connects to.

Math wizards might want to take a closer look at the technical analysis by Peter Eckersley.

There is a mathematical quantity which allows us to measure how close a fact comes to revealing somebody’s identity uniquely. That quantity is called entropy, and it’s often measured in bits. Intuitively you can think of entropy being generalization of the number of different possibilities there are for a random variable: if there are two possibilities, there is 1 bit of entropy; if there are four possibilities, there are 2 bits of entropy, etc. Adding one more bit of entropy doubles the number of possibilitie

The EFF has created a script on a website that computes how unique and trackable a web browser is.

The script will calculate a uniqueness score based on the data that the web browser reveals during connections. Tests with Google Chrome 5, Opera 10.5 pre-alpha, Internet Explorer 8 and Mozilla Firefox 3.6 revealed that all four web browsers contained unique bits that could be used to identify them.

This can be attributed to the web browser fingerprint database of the service as it contains only 450,000 fingerprints. It is likely that an increase here will reduce the uniqueness.

The self-defense aid lists some of the features that one could use to defend against browser fingerprinting:

• Try to use a “non-rare” browser
• Disable JavaScript (please note, Javascript needs to be enabled for the test to work)
• Use TorButton
• A Better Solution: Browsers’ “Private Browsing” Modes

The interesting aspect of this theory is that it is possible to track computers even if cookies have been deactivated in the web browser. There is another option to switching to a non-rare browser though: Browser switching. Identification is only possible for a session in which the same web browser is used. That in combination with disabled JavaScript could prove to be an effective defense against web browser tracking. (found at the Oracle)