Facebook has roughly 900 million users and the social network is constantly being flooded by spammers. The Verge interviewed Facebook’s security experts to find out how the social network remains protected.
Facebook regularly scans PasteBin every week to make sure that hackers are not dumping unauthorized data there. Third party websites that receive traffic from Facebook after someone clicks the “Like” button cannot see the referral URLs. In their analytics, they will see a link like “facebook.com/l.php?u=http%3A%2F%2F.”
Facebook also actively filters friend requests. The company uses an algorithm to decide the likelihood that you know somebody and whether or not to push through a friend request or file it as spam inside of the “See All Friend Requests” folder.