A new JavaScript that makes it very hard to avoid being tracked on the internets. The site below will "evercookie" you with a harmless example if you elect to take it.

It's not impossible to clean up or avoid, but it ain't so easy either. The simplest prevention that I can think of is to use the Noscript add-on in Firefox.

Safari, Chrome and Firefox should be unaffected while in private or incognito mode, but not in regular mode.

Chrome is the easiest to clean up because its cookie manager integrates flash cookies with the garden variety.

In IE you are helplessly owned, as far as I know. I'm tempted to start running my browser in a Virtual Machine that gets restarted a lot.

http://samy.pl/evercookie/