According to Facebook, 50 million people may have been affected in a data breach that happened in the past few days. The security breach came from unknown sources and it is not known if they were targetting specific accounts.

Hackers exploited a bug that took advantage of the "View As" function on Facebook, where you can view your profile as others see it. From there they were able to exploit access tokens that made Facebook think that you were the one logging in and then the hackers would potentially be able to get into your account.

Facebook logged more than 90 million people out of their accounts and forced them to log back in. They also informed law enforcement of the breach. This may have fixed the issue, and they are not aware of any accounts that were misused. Some concerns are the 3rd party apps that people access through their Facebook accounts, something to keep in mind going forward.

One tip that was mentioned, to avoid hackers, make sure you are logging out of your account when you are not using, including on your mobile devices. If you are like me, Facebook is logged in and running in the background, even when I am not actively using it. It is also a good idea to reset your passwords, in order to make it harder to hack into. Also, don't use the same passwords for everything especially your banking and financial information.

Here is the statement from Facebook:

By Guy Rosen, VP of Product Management

On the afternoon of Tuesday, September 25, our engineering team discovered a security issue affecting almost 50 million accounts. 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.

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.

Here is the action we have already taken. First, we’ve fixed the vulnerability and informed law enforcement.

Second, we have reset the access tokens of the almost 50 million accounts we know were affected to protect their security. We’re also taking the precautionary step of resetting 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. After they have logged back in, people will get a notification at the top of their News Feed explaining what happened.

Third, we’re temporarily turning off the “View As” feature while we conduct a thorough security review.

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.

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. In addition, if we find more affected accounts, we will immediately reset their access tokens.

People’s privacy and security is incredibly important, and we’re sorry this happened. It’s why we’ve taken immediate action to secure these accounts and let users know what happened. There’s no need for anyone to change their passwords. But people who are having trouble logging back into Facebook — for example because they’ve forgotten their password — should visit our Help Center. And if anyone wants to take the precautionary action of logging out of Facebook, they should visit the “Security and Login” section in settings. It lists the places people are logged into Facebook with a one-click option to log out of them all."