Updated, 2:15 p.m.

Mistakes are bound to happen in the news business, but some are worse than others.

What I’ll lay out here was a bad one. It involved a failure of sufficient skepticism at every level of the reporting and editing process — especially since the story in question relied on anonymous government sources, as too many Times articles do.

Here’s the background: A Times article Sunday reported that the U.S. government had missed something that was right out there in the open: the jihadist social-media posts by one of the San Bernardino killers. Its initial paragraphs read as follows:

Tashfeen Malik, who with her husband carried out the massacre in San Bernardino, Calif., passed three background checks by American immigration officials as she moved to the United States from Pakistan. None uncovered what Ms. Malik had made little effort to hide — that she talked openly on social media about her views on violent jihad. She said she supported it. And she said she wanted to be a part of it.

It was certainly damning – and it was wrong. On Wednesday, the F.B.I. director, James B. Comey, referred to such reporting as “a garble.” And, as it turns out from his statements and from further reporting, Ms. Malik had not posted “openly” on social media. She had written emails; she had written private messages, not visible to the public; and she had written on a dating site.

In other words, the story’s clear implication that those who vetted Ms. Malik’s visa had missed the boat – a clearly visible ocean liner – was based on a false premise.

On Thursday evening, an editors’ note was appended to the article; it appeared in Friday’s paper. Editors’ notes are sometimes used instead of corrections to provide more context and explanation. But there’s no question that this also functioned as a correction.

Even before the editors’ note appeared, readers were writing to me with their concerns. Nancy Cadet, who described herself as a longtime subscriber, wanted to know how this happened: “Were these reporters relying on tips from a non-credible source?” And she observed, quite correctly, that harm is done when The Times gets it wrong: “The falsehoods and their repercussions live on long after the stories have been corrected or disputed.”

She’s right. Erik Wemple of The Washington Post, who wrote early and often on this all week, noted that the story “set fire to the news system. All sorts of follow-up reports surfaced. And straight into the political arena it went.” It wasn’t long, he added, before Republican presidential candidate Ted Cruz was using it to bash Democrats. And there’s been a lot of commentary: Esquire saw “source pollution” as the problem; Mother Jones wrote that two of the reporters should be “considered on probation” (not dismissed, as an earlier version of this post said); and Salon called it “an epic reporting fail” with dire national consequences.

I have two major and rather simple questions: How did this happen? And how can The Times guard against its happening again? (As many readers have noted, some very critically, two of the authors of this article, Matt Apuzzo and Michael S. Schmidt, also wrote the flawed story in July that reported that Hillary Clinton would be the target of a criminal investigation by the Justice Department because of her email practices while secretary of state. Reporting by the third reporter on the current article, Julia Preston, who covers immigration, was restricted to the visa-vetting process.)

I talked on Friday to the executive editor, Dean Baquet; to one of his chief deputies, Matt Purdy; and to the Washington editor, Bill Hamilton, who edited the article. All described what happened as deeply troubling. Mr. Baquet said that some new procedures need to be put in place, especially for dealing with anonymous sources, and he said he would begin working on that immediately.

“This was a really big mistake,” Mr. Baquet said, “and more than anything since I’ve become editor it does make me think we need to do something about how we handle anonymous sources.”

He added: “This was a system failure that we have to fix.” However, Mr. Baquet said it would not be realistic or advisable to ban anonymous sources entirely from The Times.

How did this specific mistake happen?

“Our sources misunderstood how social media works and we didn’t push hard enough,” said Mr. Baquet, who read the article before publication. He said those sources apparently did not know the difference between public and private messages on social-media platforms.

I asked him why reporters or editors had not insisted on seeing or reading the social media posts in question, or even having them read aloud to them; he told me he thought that this would have been unrealistic under the circumstances, but that without that kind of direct knowledge, more caution was required.

Mr. Purdy said “we need to have a red flag” on such stories. He said he believed The Times has an “overreliance” on anonymous sources. Mr. Hamilton sees another lesson, too. “When we don’t know the details, as we didn’t here, there’s probably a reason for that,” he said. He added: “We didn’t see the dangers.”

All the editors said that slowing down, despite the highly competitive nature of a hot news story, is a necessary measure.

Mr. Baquet staunchly defended Mr. Schmidt and Mr. Apuzzo (who, he noted, won a Pulitzer Prize for investigative reporting at The Associated Press on the New York police’s surveillance of Muslims), calling them “really fine reporters who have broken a lot of great stories” in recent months. Mr. Hamilton agreed, and noted that Mr. Apuzzo and Mr. Schmidt cover two of the most sensitive beats in Washington — national security and law enforcement, respectively, including the F.B.I.

Mr. Baquet rejected the idea that the sources had a political agenda that caused them to plant falsehoods. “There’s no reason to think that’s the case,” he said.

The Times needs to fix its overuse of unnamed government sources. And it needs to slow down the reporting and editing process, especially in the fever-pitch atmosphere surrounding a major news event. Those are procedural changes, and they are needed. But most of all, and more fundamental, the paper needs to show far more skepticism – a kind of prosecutorial scrutiny — at every level of the process.

Two front-page, anonymously sourced stories in a few months have required editors’ notes that corrected key elements – elements that were integral enough to form the basis of the headlines in both cases. That’s not acceptable for Times readers or for the paper’s credibility, which is its most precious asset.

If this isn’t a red alert, I don’t know what will be.