In Facebook, cookie owns you.
An Australian hacker Nik Cubrilovic has uncovered a security flaw with cookies generated by Facebook logins that causes them to continue tracking users even after they have logged out.
It was found that Facebook does not delete all cookies after a log-out, instead creates three new ones and gives two more an extended expiry date. The cookies then continues to track users, and sends Facebook information on every site that features the Facebook Like or Share button.
Cubrilovic believes that Facebook uses the information to suggest friends, however it could be potentially dangerous “If you login on a public terminal and then hit ‘logout’, you are still leaving behind fingerprints of having been logged in. As far as I can tell, these fingerprints remain (in the form of cookies) until somebody explicitly deletes all the Facebook cookies for that browser.”
Users are suggested to delete all cookies pertaining to Facebook after they are done with their business. Chrome users can simply use Facebook Disconnect extension to perform the task; Firefox users has Ghostery for it.