WASHINGTON — A former security chief at Twitter told Congress on Tuesday that the social platform is plagued by weak cyber defenses, privacy threats and the inability to control millions of fake accounts. Peiter “Mudge” Zatko, a respected cybersecurity expert, appeared before the Senate Judiciary Committee to lay out his allegations.

“Twitter’s misleading the public, lawmakers” and regulators, Zatko said as he began his sworn testimony.

“They don’t know what data they have, where it lives and where it came from and so, unsurprisingly, they can’t protect it,” Zatko said. “It doesn’t matter who has keys if there are no locks.”

Zatko said “Twitter leadership ignored its engineers,” in part because “their executive incentives led them to prioritize profit over security.” His message echoed one brought to Congress against another social media giant last year, but unlike that Facebook whistleblower, Frances Haugen, Zatko hasn’t brought troves of internal documents to back up his claims.

Zatko was the head of security for the influential platform until he was fired early this year. He filed a whistleblower complaint in July with Congress, the Justice Department, the Federal Trade Commission and the Securities and Exchange Commission. Among his most serious accusations is that Twitter violated the terms of a 2011 FTC settlement by falsely claiming that it had put stronger measures in place to protect the security and privacy of its users.

Senators are clearly alarmed.

Sen. Dick Durbin, an Illinois Democrat who heads the Judiciary Committee, said Zatko has detailed flaws “that may pose a direct threat to Twitter’s hundreds of millions of users as well as to American democracy.”

“Twitter is an immensely powerful platform and can’t afford gaping vulnerabilities,” he said.

Zatko’s claims could also affect Tesla billionaire Elon Musk’s attempt to back out of his $44 billion deal to acquire the social platform. Musk claims that Twitter has long underreported spam bots on its platform and cites that as a reason to nix the deal he struck in April.

Many of Zatko’s claims are uncorroborated and appear to have little documentary support. Twitter has called Zatko’s description of events “a false narrative … riddled with inconsistencies and inaccuracies” and lacking important context.

Zatko also accuses the company of deception in its handling of automated “spam bots,” or fake accounts. That allegation is at the core of billionaire tycoon Elon Musk’s attempt to back out of his $44 billion deal to buy Twitter. Musk and Twitter are locked in a bitter legal battle, with Twitter having sued Musk to force him to complete the deal. The Delaware judge overseeing the case ruled last week that Musk can include new evidence related to Zatko’s allegations in the high-stakes trial, which is set to start Oct. 17.

Sen. Charles Grassley, the committee’s ranking Republican, said Tuesday that Twitter CEO Parag Agrawal declined to testify at the hearing, citing the ongoing legal proceedings with Musk. But the hearing is “more important that Twitter’s civil litigation in Delaware,” Grassley said.

In his complaint, Zatko accused Agrawal as well as other senior executives and board members of numerous violations, including making “false and misleading statements to users and the FTC about the Twitter platform’s security, privacy and integrity.”

Zatko, 51, first gained prominence in the 1990s as an ethical hacker and later worked in senior positions at an elite Defense Department research unit and at Google. He joined Twitter in late 2020 at the urging of then-CEO Jack Dorsey.