Facebook - New Logon Security improvements
Facebook users can now specifically define computers they want to login with. Controls were also added to block unauthorized attempts to unusual devices as noted below.
Facebook Strengthens Logon Security
QUOTE: Login Notifications - Over the last few weeks, we’ve been testing a new feature that allows you to approve the devices you commonly use to log in and then to be notified whenever your account is accessed from a device you haven’t approved. This feature is now available to everyone. Facebook has also done some tuning/magic on their side to block bogus or questionable logon attempts. If they see logons from unusual devices, they will prompt those users with additional verification questions, in essence, making them prove they are who they say they are.