Facebook Security Breach Exposes Accounts

“We’re taking it really seriously,” Mr. Zuckerberg, the chief executive, said in a conference call with reporters. “I’m glad we found this, but it definitely is an issue that this happened in the first place.”

Critics say the attack is the latest sign that Facebook has yet to come to terms with its problems. filtertechnik.mobi

“Breaches don’t just violate our privacy. They create enormous risks for our economy and national security,” Rohit Chopra, a commissioner of the Federal Trade Commission, said in a statement. “The cost of inaction is growing, and we need answers.”

Facebook has been roundly criticized for being slow to acknowledge a vast disinformation campaign run by Russian operatives on its platform and other social media outlets before the 2016 presidential election.

Ms. Sandberg, Facebook’s chief operating officer, testified in a Senate hearing that month about what the company was trying to do to prevent the same thing from happening in midterm elections in November.

In April, Mr. Zuckerberg testified about revelations that Cambridge Analytica, the British analytics firm that worked with the Trump presidential campaign, siphoned personal information of millions of Facebook users.

Outside the United States, the impact of disinformation appearing on Facebook and the popular messaging service it owns, WhatsApp, has been severe. In countries such as Myanmar and India, false rumors spread on social media are believed to have led to the widespread killing.

Facebook said the attackers had exploited two bugs in the site’s “View As” feature, which allows users to check on what information other people can see about them. The feature was built to give users move control over their privacy.