Facebook says 50 million user accounts affected by security breach

Social network does not know who is behind the breach and has informed law enforcement; 90 million users will have their logins reset

Facebook said Friday it recently discovered a security breach affecting nearly 50 million user accounts.

The hack is the latest setback for Facebook during a year of tumult for the global social media service.

In a blog post, the company said hackers exploited its “View As” feature, which lets people see what their profiles look like to someone else. Facebook said it has taken steps to fix the security problem and alerted law enforcement.

The social network said it learned this week of the attack that allowed hackers to steal “access tokens,” the equivalent of digital keys that enable them to access their accounts.

“It’s clear that attackers exploited a vulnerability in Facebook’s code,” vice president of product management Guy Rosen said in the post.

“We’ve fixed the vulnerability and informed law enforcement.”

To deal with the issue, Facebook reset some logins, so 90 million people have been logged out and will have to log in again. That includes anyone who has been subject to a “View As” lookup in the past year.

Facebook said it doesn’t know who is behind the attacks or where they’re based.

News broke early this year that a Trump-linked data analytics firm, Cambridge Analytica, had gained access to personal data from millions of user profiles. Then a congressional investigation found that agents from Russia and other countries have been posting fake political ads since at least 2016. Facebook CEO Mark Zuckerberg appeared at a Congressional hearing over Facebook’s privacy policies in April.

In a call with reporters on Thursday Zuckerberg said that the company doesn’t know yet if any of the accounts that were hacked were misused.

Facebook has more than 2 billion users worldwide.