Originally Posted by Cabbs
It could have been 3 years since he logged on.
Well most facebook accounts that are stolen "hacked" are from key-logging and phishers. Both of those methods require the user to enter the information thus making this rather strange.
This could be a couple things..
1. Someone impersonating facebook (phishing).
2. Someone hacked your email account and seen an email from facebook.
Then either you had the same password for facebook, or they used the reset password feature.