50 million users affected in Facebook security breach

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Mark Zuckerberg's Facebook was the target of an online attack this week, affecting 50 million users.
Mark Zuckerberg's Facebook was the target of an online attack this week, affecting 50 million users.

The world's largest social network announced this evening that 50 million of its users were affected by a security breach that occurred earlier this week on Tuesday, 25 September.

Facebook says it has sorted the issue, but as a result many users will find they have to sign back into their accounts this weekend.

"We're taking this incredibly seriously and wanted to let everyone know what's happened and the immediate action we've taken to protect people's security," says Guy Rosen, Facebook VP of product management.

"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. 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."

Earlier this year the company reached two billion monthly active users for its main Facebook platform.

In a post on Facebook, CEO Mark Zuckerberg said: "We do not yet know whether these accounts were misused but we are continuing to look into this and will update when we learn more."

Rosen says the vulnerability has been fixed and law enforcement has been informed.

He says all 50 million accounts affected have had their tokens reset, as well as a further 40 million accounts that have been subject to a 'View As' look-up in the last year.

"As a result, around 90 million people will now have to log back in to Facebook, or any of their apps that use Facebook Login. After they have logged back in, people will get a notification at the top of their News Feed explaining what happened."

The company says it will also be temporarily turning off the 'View As' feature while they conduct a thorough security review.

Rosen says the attack exploited the complex interaction of multiple issues in Facebook's code.

"It stemmed from a change we made to our video uploading feature in July 2017, which impacted 'View As'. The attackers not only needed to find this vulnerability and use it to get an access token, they then had to pivot from that account to others to steal more tokens.

"Since we've only just started our investigation, we have yet to determine whether these accounts were misused or any information accessed. 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."

He says that if more affected accounts are found their access tokens will also be immediately reset.

"People's privacy and security is incredibly important, and we're sorry this happened," says Rosen.

He says there is no need for anyone to change their passwords, but users who are having trouble logging back into Facebook, for example because they've forgotten their password, should visit the site's Help Centre.

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