Facebook Bug Changed Privacy Settings of Up to 14 Million Users

SAN FRANCISCO — Facebook has been fighting for months the perception it did not do enough to protect people’s privacy. On Thursday, the company said it had again failed to keep the information of millions of users private.

As many as 14 million Facebook users who thought they were creating private posts last month that only a small group of friends could see were, in fact, making public posts that anyone could view.

Facebook blamed a software bug for the problem. The company did not say how it had found the bug, or how it knew the problem was limited to 14 million people.

In a statement, Facebook said the bug affected users from May 18 to May 22, while the company was testing a new feature. By May 27, the company had changed the affected posts from a public setting back to a private one.

In the last few months, Facebook executives have repeatedly been forced to apologize to users for failing to protect their privacy.

In March, The New York Times reported that the data of more than 87 million people had been collected by Cambridge Analytica, a political firm with ties to the Trump campaign. This week, The Times reported that Facebook had given cellphone makers, including Apple, Samsung and the Chinese firm Huawei, access to data on Facebook users and their friends. Members of Congress are now questioning Facebook and other tech companies about their relationship to Huawei.

Trust in Facebook has fallen 66 percent as a result of news stories in recent months, according to a survey by the Ponemon Institute, an independent research firm specializing in privacy and data protection.

In response to the problems, the company has added a number of new privacy controls, as well as a centralized page for privacy and security settings.

One of Facebook’s key privacy features is that it lets people decide an audience for their posts. Someone can, for example, share a post with only a limited group of family and friends, or decide to make a post public so that anyone, including people not logged on to Facebook, can see it.

It was unclear if users could have done anything to their settings to prevent being affected by the bug the company announced Thursday.