It’s no secret that Facebook and privacy have had some issues. Take today, for example. Thanks to a modified cookie, Facebook knows where you are online—even when you’re not logged into Facebook.
So says hacker Nik Cubrilovic anyway, after he discovered during a series of tests that Facebook alters its tracking cookie code the moment you log out, instead of deleting them. Then, when a user being tracked in this manner heads to a web site that contains a Facebook button or widget, the browser continues to send "personally identifiable information" back to Facebook.