It seems that Facebook is actually not using cookies to track you. At least not after you log out. Users, however, should still be wary about what Facebook knows about them and what it chooses to do with this information.
According to writer and hacker, Nik Cubrilovic, Facebook’s tracking cookies are not deleted when you log out of Facebook, but instead are simply altered. These cookies can then be used to track your online presence wherever you go via social plugins, to sell your information to third parties and for ad targeting.
Facebook has recently responded to these allegations via a comment on ZDNet. A Facebook engineer denied that Facebook is using these altered cookies as a source of information, but says they are instead used to protect users against hackers, prevent underage users from trying to re-register and to identify shared computers (again, to protect users who choose the “keep me logged in” option).
Even if this is true, we should all keep in mind that cookies can definitely be used for tracking. For example, if you log on to Facebook from a public computer, your account information stays on that computer even after you log out. What this information is used for by Facebook is one thing, but your tracks are not covered.
Also keep in mind that one of Facebook’s new features, frictionless sharing, will automatically share in your newsfeed any article you read which has the Facebook plugin. No active clicking involved – it will just happen. Another good reason to stay logged out of your account while you’re surfing.