SAN FRANCISCO — Confronted with a ballooning crisis over his company’s commitment to being a steward of people’s personal information, Facebook’s chief executive, Mark Zuckerberg, said on Wednesday that the social network had made mistakes and that it was taking action to prevent users’ data from being improperly harvested.
While Mr. Zuckerberg stopped short of a full-throated apology and was at times defensive, his Facebook post said that the Silicon Valley company must step up and do more to protect the information of its users.
“We have a responsibility to protect your data, and if we can’t then we don’t deserve to serve you,” Mr. Zuckerberg wrote.
The statement was the first time that Mr. Zuckerberg, 33, has spoken publicly since The New York Times reported over the weekend that Cambridge Analytica, a political consulting firm that provided voter-targeting services to Donald J. Trump’s presidential campaign, had improperly obtained data on 50 million Facebook users.
Those revelations were just the latest to raise red flags about Facebook’s handling of user data and security, and came after the company has faced intense criticism over Russian manipulation of the platform before and after the 2016 presidential election as well as the rise of misinformation on the site.
The resulting backlash has thrust Facebook into its worst crisis since it was founded in 2004. The information, photos and other content that users post and their frequent engagement with the platform is crucial to the social network, and its business. Questions about user privacy and security threaten to derail that mission, at a time when people are already concerned about whether the use of technology can bring good or ill.
The reaction has been severe. Politicians in the United States and in Britain have called for Mr. Zuckerberg to explain how his company handles user data, and state attorneys general in Massachusetts and New York have begun investigating Cambridge Analytica and Facebook. A #DeleteFacebook movement calling on people to close their accounts has also gathered steam among users who have lost confidence that the company is trustworthy in collecting — and safeguarding — their data.
Inside Facebook, even staunch supporters of Mr. Zuckerberg have described a tense atmosphere. Some employees have sought to transfer to other divisions, such as the messaging app WhatsApp and the photo-sharing platform Instagram, calling their work on Facebook’s main product “demoralizing.”
Mr. Zuckerberg spent part of the past week hunkered down with a small group of engineers to discuss how to make information on Facebook’s users more secure, and to potentially give them more control of their data, according to two Facebook employees who declined to be named because the proceedings were confidential.
His silence on the matter has prompted mounting criticism in the past few days. While Facebook held a staff meeting on Tuesday to answer questions about Cambridge Analytica and the surrounding outcry, Mr. Zuckerberg did not appear at the event.
On Wednesday, Mr. Zuckerberg said in his post that Facebook would investigate apps that had access to “large amounts of information” from the social network before it made a policy change in 2014 and clamped down on some of the data access. He also said the company would restrict developers’ data access to the social network.
In addition, Mr. Zuckerberg said there should be more disclosure about the apps that people have used and how to revoke the apps’ permission to that data. Mr. Zuckerberg said a tool would be rolled out in the next month that would make that information more transparent.
“We also made mistakes, there’s more to do, and we need to step up and do it,” he wrote.