Facebook has discovered a security breach affecting almost 50 million accounts.
"Our investigation is still in its early stages. But it’s clear that attackers exploited a vulnerability in Facebook’s code that impacted “View As”, a feature that lets people see what their own profile looks like to someone else," the company said in a statement issued Friday. "This allowed them to steal Facebook access tokens which they could then use to take over people’s accounts. Access tokens are the equivalent of digital keys that keep people logged in to Facebook so they don’t need to re-enter their password every time they use the app."
Facebook says it has fixed the vulnerability, informed law enforcement and is reviewing its security. The engineers have also reset the access tokens to protect the security of the affected accounts. Facebook is also resetting access tokens for another 40 million accounts that have been subject to a “View As” look-up in the last year.
"Since we’ve only just started our investigation, we have yet to determine whether these accounts were misused or any information accessed," Facebook said. "We also don’t know who’s behind these attacks or where they’re based. We’re working hard to better understand these details — and we will update this post when we have more information, or if the facts change. In addition, if we find more affected accounts, we will immediately reset their access tokens."
Around 90 million people will now have to log back in to Facebook or any of their apps that use Facebook Login. People will get a notification at the top of their News Feed explaining what happened after they have logged back in.