Fighting the Evercookie

The next front in the cookie wars: Fighting the Evercookie

• Date: November 1st, 2010
• Author: Michael Kassner

Samy Kamkar: Evercookie is a Javascript API that allows storing cookie data in a number of different locations when a user visits a web page. Normal sites would typically just store data (such as a session identifier) in something like a cookie.

However, Evercookie not only uses the cookie, but a number of other locations such as Flash cookies, Silverlight isolated storage, and various locations of HTML5 storage. When a user deletes their standard cookies, the other locations remain and are able to rebuild the original cookie.

I built Evercookie as a proof of concept, wanting to show how web sites are able to track users even if they delete standard cookies and LSOs. Evercookie also sheds light on the fact that there are numerous methods for storing cookies locally. Finally, Evercookie acts as a litmus test for users who want to see if they’re protected from web sites that track like this.