Over half of the most popular 100 websites use secret behaviour-tracking software to monitor users, mostly without their knowledge, and in several cases the software recovers information the user has chosen to delete.
Small pieces of identifying code hidden in Adobe's near-ubiquitous Flash media player can be used to track users' behaviour. The pieces of code behave similarly to 'standard' cookies and are known as Flash cookies.
Researchers at the University of California, Berkeley have discovered that Flash cookies can measure and report the behaviour of users even when those users have disabled or deleted standard, or HTTP, cookies. It found that several of the most popular 100 websites have Flash cookies which 'respawn' HTTP cookies, meaning they store information and write it into HTTP cookies on a person's revisit to that site, even if that person has told their computer to delete HTML cookies.
Source: Out-Law.com
