Logging out of Facebook is not enough
rten:
If you’re concerned of privacy remember that just logging out of Facebook is not enough, you can be tracked while you’re logged out. Whether this is being done in reality is something we can only speculate on.
Nic Cubrilovic: The primary cookies that identify me as a user are still there (act is my account number), even though I am looking at a logged out page. Logged out requests still send nine different cookies, including the most important cookies that identify you as a user
This is not what ‘logout’ is supposed to mean - Facebook are only altering the state of the cookies instead of removing all of them when a user logs out.
With my browser logged out of Facebook, whenever I visit any page with a Facebook like button, or share button, or any other widget, the information, including my account ID, is still being sent to Facebook. The only solution to Facebook not knowing who you are is to delete all Facebook cookies.