A neat little tidbit about Facebook security in this post from The Verge. Good Guy Facebook proactively scans lists of hijacked account and warns users if they appear on one of these lists.
Facebook cross references credential dumps with its entire database of user credentials, then alerts any users that match to change their passwords. By signing up for Facebook, you’ve inadvertently entered yourself into its witness protection program, of sorts. During events like the Gawker credentials leak or Playstation Network security breach last year, Facebook alerted users if their passwords were on the loose.
via The Verge