Tech giant Facebook says that there was a major security breach where 50 million user accounts were accessed by unknown attackers.
The attackers gained the ability to "seize control" of those accounts, Facebook said, by stealing digital keys the company uses to keep people logged in.
Facebook has logged out owners of the 50 million affected accounts — plus another 40 million who were vulnerable to the attack.
Users don't need to change their Facebook passwords.
Facebook doesn't know who was behind the attacks or where they're based.