Facebook said it logged out around 90 million users as a result of the hack.
Affected users will be prompted to log back in Facebook when they try and access the site.
Users are sent a six-digit code via email or to a mobile device that authenticates their identity, which they’re then instructed to enter on Facebook’s site.
After they have logged back in, people will get a notification at the top of their News Feed explaining what happened.
Facebook also said it was temporarily turning off the ‘View As’ feature while it conducted a thorough security review.