Just months after he faced the US Senate over the Cambridge Analytical Crisis, Mark Zuckerberg found himself in the midst of yet another storm. Facebook admitted that its company was affected by yet another data breach this time affecting at least 50 million of its users.

The company issued a statement that said,’ our engineering team discovered a security issue affecting almost 50 million accounts. 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.’

So what is access token? Facebook explained, ‘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 has reset the access tokens of the almost 50 million accounts and as a precautionary step they have also reset access tokens for another 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.

Facebook has also turned off their “View As” feature for the time being . Facebook believes this comes after they reset video uploading feature in July last years.

Reacting to the controversy, Founder and CEO Mark Zuckerberg said, ‘We do not yet know whether these accounts were misused. We patched the security vulnerability to prevent this attacker or any other from being able to steal additional access tokens. And we invalidated the access tokens for the accounts of the 50 million people who were affected – causing them to be logged out. We do not currently have any evidence that suggests these accounts have been compromised, but we’re taking this step as a precautionary measure.’

Reports suggest that FBI and Irish agencies may have been roped in to investigate this hack.