"If I had not explicitly signed-out of Facebook before visiting all these other sites, Facebook knows about it." Even if you have explicitly signed-out of Face

"If I had not explicitly signed-out of Facebook before visiting all these other sites, Facebook knows about it." Even if you have explicitly signed-out of Facebook, the presence of the like button on a site allows Facebook to track your movements on that site. Their like button javascript reports back a unique login cookie that is not erased when you sign off of Facebook. Pressing the like button is a small part of its purpose. Its purpose is to track you around the web as long as you have ever logged into Facebook before. This was all covered here on HN months ago, when I first learned of it.