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How hackers accessed data from 29 million Facebook accounts

Staff Writer |
Facebook says hackers accessed data from 29 million accounts as part of the security breach disclosed two weeks ago.

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The exact number hadn’t been known before. Originally Facebook said 50 million accounts could have been affected, but Facebook didn’t know if they had been misused.

The hackers accessed name, email addresses or phone numbers from those 29 million accounts.

For 14 million of those accounts, hackers got even more data, such as hometown, birthdate, the last 10 places they checked into or 15 most recent searches. One million accounts were affected but hackers didn’t gain information. The social media service plans to send messages to people whose accounts were hacked.

"As we’ve said, the attackers exploited a vulnerability in Facebook’s code that existed between July 2017 and September 2018," Facebook says.

"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 profile looks like to someone else.

"It allowed attackers 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’s how we found the attack that exploited this vulnerability. We saw an unusual spike of activity that began on September 14, 2018, and we started an investigation," Facebook says.

"On September 25, we determined this was actually an attack and identified the vulnerability.

"Within two days, we closed the vulnerability, stopped the attack, and secured people’s accounts by resetting the access tokens for people who were potentially exposed. As a precaution, we also turned off “View As.” We’re cooperating with the FBI, which is actively investigating and asked us not to discuss who may be behind this attack.

"We now know that fewer people were impacted than we originally thought. Of the 50 million people whose access tokens we believed were affected, about 30 million actually had their tokens stolen. Here’s how it happened:

"First, the attackers already controlled a set of accounts, which were connected to 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.

"In the process, however, this technique automatically loaded those accounts’ Facebook profiles, mirroring what these 400,000 people would have seen when looking at their own profiles.

"That includes posts on their timelines, their lists of friends, Groups they are members of, and the names of recent Messenger conversations.

"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.

"The attackers used a portion of these 400,000 people’s lists of friends to steal access tokens for about 30 million people.

For 15 million people, attackers accessed two sets of information – name and contact details (phone number, email, or both, depending on what people had on their profiles).

"For 14 million people, the attackers accessed the same two sets of information, as well as other details people had on their profiles.


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