Social networking website Facebook has said it prevents at least 600,000 attempts every day by hackers trying to break into user accounts, using stolen usernames and passwords.
http://ummid.com/news/2011/October/29.10.2011/hacking_attempt_on_facebook.htm
http://ummid.com/news/2011/October/29.10.2011/hacking_attempt_on_facebook.htm