Facebook accounts faces security issue: How to check whether your account is safe and if you need to change passwordSep 28 (AZINS) Facebook on Friday disclosed a security flaw which could have allowed 50 million accounts to be taken over by hackers.The large 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 a blog post. "We've fixed the vulnerability and informed law enforcement."

Facebook said that the vulnerability was discovered on Tuesday and now the issue has been resolved. However, it is so far uncertain whether any data has been misused or not. According to Facebook, it changed the 'access token' for nearly 90 million users. Out of which there are 50 million accounts which were said to be hacked and 40 million additional accounts for safety purpose. Those accounts have been logged out and asked to log in from web, mobile or app, wherever the user was using it.

So if you have been auto-logged out, then your account's 'access token' has been changed. However, according to Facebook, you don't need to change password as they have sorted out the glitch. Once they logged in, there will be a notification at top of News Feed explaining what has happened.

Here's the full blog from Facebook written 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.