One of the challenges for Facebook’s chief executive Mark Zuckerberg is convincing users that the company handles their data responsibly.CreditCreditJosh Edelson/Agence France-Presse — Getty Images

By Mike Isaac and Sheera Frenkel

Sept. 28, 2018

SAN FRANCISCO — Facebook, already facing scrutiny over how it handles the private information of its users, said on Friday that an attack on its computer network had exposed the personal information of nearly 50 million users.

The breach, which was discovered this week, was the largest in the company’s 14-year history. The attackers exploited a feature in Facebook’s code to gain access to user accounts and potentially take control of them.

The news could not have come at a worse time for Facebook. It has been buffeted over the last year by scandal, from revelations that a British analytics firm got access to the private information of up to 87 millionusers to worries that disinformation on Facebook has affected elections and even led to deaths in several countries.

Senior executives have testified several times this year in congressional hearings where some lawmakers suggested that the government will need to step in if the social network is unable to get tighter control of its service. On Friday, regulators and lawmakers quickly seized on the breach to renew calls for more oversight.

“This is another sobering indicator that Congress needs to step up and take action to protect the privacy and security of social media users,” Senator Mark Warner, a Democrat from Virginia and one of Facebook’s most vocal critics in Congress, said in a statement. “A full investigation should be swiftly conducted and made public so that we can understand more about what happened.”

In the conference call on Friday, Guy Rosen, a vice president of product management at Facebook, declined to say whether the attack could have been coordinated by hackers supported by a nation-state.

Three software flaws in Facebook’s systems allowed hackers to break into user accounts, including those of the top executives Mark Zuckerberg and Sheryl Sandberg, according to two people familiar with the investigation but not allowed to discuss it publicly. Once in, the attackers could have gained access to apps like Spotify, Instagram and hundreds of others that give users a way to log into their systems through Facebook.

The software bugs were particularly awkward for a company that takes pride in its engineering: The first two were introduced by an online tool meant to improve the privacy of users. The third was introduced in July 2017 by a tool meant to easily upload birthday videos.

Facebook said it had fixed the vulnerabilities and notified law enforcement officials. Company officials do not know the identity or the origin of the attackers, nor have they fully assessed the scope of the attack or if particular users were targeted. The investigation is still in its beginning stages.