50 million Facebook accounts were hacked this week, via a flaw in the "View as" feature on there.
This gave hackers full access to any account they wanted. 50 million accounts were targeted this way (obviously through an automated process), and Facebook forcibly logged out another 40 million as a precaution.
If your account was automatically logged out this week, there's a 55.5% chance your account had been hacked.
Facebook refuses to tell anyone if they were among those hacked, but the forcible logout is a clue.
It does not appear that the hackers know anyone's passwords.
However, the hackers DID have access to any sites where people log in through their Facebook account. This is one of many reasons I always advise people, "Gotta keep 'em separated", and never to link social media logins to other sites and services.
It is likely that all of your personal information, friends lists, and private messages were accessible to the hackers. However, as this was an automated process where 50 million accounts were breached, it is unlikely you will be individually targeted in any way, unless data dumps are done in the future.
If you are sure that you never used the "View As" feature in the past year, and your account was forcibly logged out, then you were hacked.
If you HAVE used "View As" in the past year, then it is inconclusive whether you were hacked or not, as Facebook force-logged-out anyone who has used that feature in the past year, whether they were hacked or not.
I find it offensive that Facebook will not inform the 50 million victims that they were hacked, for their own knowledge.