Facebook has reset the access to 90 million user accounts after finding a security breach, forcing the affected users to log back into their accounts, the company announced Friday. The breach allowed hackers to access other people’s accounts, and directly affected 50 million of those accounts.
“We patched the issue last night,” Facebook CEO Mark Zuckerberg said on a press call Friday. “We do not yet know whether any private information was accessed.”
The company said that it doesn’t yet know whether the breach was used by anyone to access any personal information, including private messages, from those 50 million Facebook users without their knowledge. It did confirm that hackers were able to access profile information, including age, gender, and place of residence, but that they didn’t have access to any credit card information.
Facebook said that it was working with the FBI and other law enforcement agencies to help investigate the breach.
“We also don’t know who’s behind these attacks or where they’re based,” Facebook’s VP of product management Guy Rosen wrote in a blog post. “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.”
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At the center of the hack was a Facebook feature that allows users to view their own Facebook page the way other users with different access levels — friends, family, or unknown users — would see it. This “view as” feature could apparently be exploited to also steal access tokens to take over third-party accounts.
“We’re temporarily turning off the ‘View As’ feature while we conduct a thorough security review,” Rosen wrote Friday. Users who have been affected by the breach will have to log back into their Facebook account, and the company said that it would post a note atop of their newsfeed explaining the situation.
Rosen explained during Friday’s call that the company inadvertently introduced three bugs when it updated changes to its video uploader in July of 2017. However, the company didn’t discover that these bugs could be used to hack its system until this week. It informed law enforcement about it on Wednesday, and disabled the vulnerability late Thursday.
The company decided to disable access tokens for another 40 million users as a precautionary measure because it found that the profiles of those users were browsed with the “view as” feature enabled. However, this could have also been a legitimate use of the feature.
Facebook does not yet know whether the hack was initiated by nation-state actors, but Rosen said Friday that the 50 million users targeted were seemingly a broad slice of Facebook’s users. The company did notify European authorities about the breach, something that it is required to do under Europe’s new privacy laws if European users were affected.
“The reality is, we face constant attacks,” Zuckerberg said during Friday’s call. He added that he was happy that this particular breach was uncovered, but that the company had to step up its security efforts going forward. “We need to prevent this from happening in the first place.”
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