As many as 90 million Facebook users will have to log back into their accounts after the social network admitted on Friday that hackers had stolen the security tokens associated with 50 million user profiles.
As a precaution, Facebook has reset the security tokens for the 50 million accounts as well as for 40 million others.
The attackers exploited Facebook's systems through a flaw in the company's "View As" feature, the company said, which allows a Facebook user to view his or her own profile as a friend, the public or another third party might see it.