During a hearing with the Senate Judiciary Committee, Twitter’s former security chief turned whistleblower, Peiter Zatko, shed new light on his claims that the company’s lax security practices harmed U.S. national security. Among the new allegations was that the company had a Chinese agent working for the country’s Ministry of State Security (MSS) on its payroll.

During his opening statement, Sen. Chuck Grassley stated that “the FBI notified Twitter of at least one Chinese agent in the company.” In the public version of his whistleblower complaint, Zatko stated he had been warned that the company was employing “one or more” people who were “working on behalf of another particular foreign intelligence agency.” But the version of the complaint made public, parts of which were redacted, didn’t specify what country the FBI was referring to.

In his testimony, Zatko confirmed the company had been warned about the presence of Chinese agents. “This was made aware to me maybe a week before I was summarily dismissed,” Zatko said. “I had been told because the corporate security/physical security team had been contacted and told that there was at least one agent of the MSS, which is one of China’s intelligence services on the payroll inside Twitter.”

Zatko also raised concerns about the presence of foreign agents from other countries, including India, which he said “forced” Twitter to hire government agents. 

Notably, Zatko’s disclosures are not the first time Twitter has had to contend with the presence of unregistered foreign agents on its payroll. A former Twitter worker was recently convicted of acting as an agent for Saudi Arabia. Prosecutors alleged the man was paid to turn over sensitive information about dissidents.

Zatko alleged that the danger posed by foreign agents was even greater due to a litany of factors: the vast amount of data the platform collects and its lack of insight into that data, as well as the broad and largely unfettered access Twitter’s engineers have to it. “It’s not far-fetched to say that an employee inside the company could take over the accounts of all of the senators in this room,” Zatko said. 

The hearing is likely to amp up the pressure on Twitter, which has so far declined to address Zatko’s claims in detail. Senator Grassley said that the committee had also invited CEO Parag Agrawal to testify at the hearing but that he had “refused to appear.”

“He rejected this committee’s invitation to appear by claiming that it would jeopardize Twitter’s ongoing litigation Mr. Musk,” Grassley said, referring to the company’s legal battle with Elon Musk over his $44 billion acquisition of the company. “Protecting Americans from foreign influence is more important than Twitter’s civil litigation in Delaware. If these allegations are true, I don’t see how Mr. Agrawal can maintain his position at Twitter going forward.”