Facebook has said they will fix a major privacy breach that allowed them to collect members browsing information after they had logged out. Australian blogger Nik Cubrilovic revealed on his blog that Facebook kept its browser cookies active after a user has logged out. He revealed that the information Facebook collected made it possible for them to personally label computer usage information that it collected from PCs and that Facebook merely alters its tracking cookies when you log out, instead of deleting them.
Facebook defended the practice on The Wall Street Journal blog Digits. They said the collection was part of a system to prevent improper logins and that the information was quickly deleted. A Facebook spokesman said "no information we receive when you see a social plug-in is used to target ads." A Facebook engineer said that Facebook uses the data from logged out cookies only to prevent spamming, phishing and other security risks.
To block Facebook from following you, you need to delete all Facebook-related cookies after logging out.