Another day, another major security breach, and even more pain for Facebook which in recent months has failed to keep up with the FANG euphoria.

Facebook said that on September 25 it discovered a security breach which affected almost 50 million accounts. The company said it’s investigating the breach, which allowed hackers to take over a person’s account.

In the statement, Facebook said 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."

This attack exploited the complex interaction of multiple issues in our 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.

The social network added that it has "yet to determine whether these accounts were misused or any information accessed." It also doesn't know "who’s behind these attacks or where they’re based."

As part of its response, the social-media network said that it has fixed the vulnerability, reset the access tokens of the almost 50 million accounts we know were affected to protect their security, turned off the "View As" feature, and told law enforcement authorities about the breach.

Shares declined over 2% percent on the news.

... with the drop enough to push the Nasdaq lower:

Full Facebook statement below: