Facebook today confirmed the actual number of users hit in its recent data breach is 30 million rather than its original estimate of 50 million.
The social media giant also is investigating other possible "smaller-scale attacks" leveraging the vulnerability in its code that was exploited in the breach, which it first reported late last month. The attackers already had control of a set of user accounts that were then connected to those users' Facebook friends.
"They used an automated technique to move from account to account so they could steal the access tokens of those friends, and for friends of those friends, and so on, totaling about 400,000 people," said Guy Rosen, vice president of product management for Facebook, in a post today.
This allowed the attackers to obtain Facebook profiles and see their timeline posts, lists of friends, groups, and names in recent Messenger chats. "Message content was not available to the attackers, with one exception. If a person in this group was a Page admin whose Page had received a message from someone on Facebook, the content of that message was available to the attackers," according to Facebook.
The FBI, which is investigating the attack, has asked the social media giant not to discuss who may be behind it.
Here's how the attack spread: The attackers used part of the 400,000 users' friends lists to steal tokens of 30 million people on Facebook. Some 15 million Facebook users' names, phone numbers, and email addresses were pilfered. For another 14 million users, their usernames and profile details – such as gender, relationship status, hometown, birthdate, city, and devices – as well as their 15 most recent searches from the platform also were stolen. That's in addition to their names, phone numbers, and email addresses.
The remaining 1 million Facebook members' information was not accessed in the attack.
'View As' Bug
Facebook last week announced that a previously unknown vulnerability in its code that existed between July 2017 and September 2018 had been exploited by attackers to steal Facebook access tokens, which could be used to hijack user accounts. Tokens are basically digital keys that allow users to remain logged into the social media platform without constantly signing in.
"The vulnerability was the result of a complex interaction of three distinct software bugs and it impacted "View As," a feature that lets people see what their own profiles look like to someone else," Rosen said.
Facebook discovered the attack on Sept. 25, after noticing unusual activity starting on Sept. 14. "Within two days, we closed the vulnerability, stopped the attack, and secured people's accounts by restoring the access tokens for people who were potentially exposed. As a precaution, we also turned off 'View As,'" Rosen said.
The company suggests Facebook users check the Help Center. It has already begun sending messages to affected victims about what information was stolen and how to protect themselves.
Note from author: While writing this story, I received a notice from Facebook today that I'm one of the breach victims: My name, email address, and phone number were accessed by the attackers.
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