Over the weekend, a hacker known as Hannibal leaked 100,000 Facebook usernames and passwords that allegedly belong to Arab users of the social network. This leak is the result of an ongoing Israeli-Arab feud and probably not a cause for concern, as Facebook believes its network wasn't hacked and most of the login credentials are invalid.
While you shouldn't panic unduly, a little checking makes sense. First, you should check if your credentials were posted by Hannibal. Second, if you haven't changed your password lately there's no time like the present. We have plenty of suggestions for picking a better one. Stay diligent, and you'll have less to worry about in the event of a more significant threat to Facebook or any other site.
Hacker releases 100,000 Facebook log-in credentials [Computerworld]