Facebook’s chief security officer Alex Stamos has left the company to become a fellow at nearby Stanford University.
His departure had been expected following news in March that Facebook was reorganising its security division.
Facebook’s chief operating officer Sheryl Sandberg said Mr Stamos had played an “important role” at the company.
Mr Stamos, 39, had been with the firm since 2015. He will leave later this month.
He does so at a time when Facebook remains under scrutiny over the spread of misinformation on its platform, as well as an ongoing data privacy crisis.
Speaking to the New York Times, Mr Stamos described his time at Facebook as a “difficult three years”.
"I’d like to take the things I’ve learned and apply them more broadly,” he said.
And in a Facebook post published on Wednesday, he added: "I have been proud to work with some of the most skilled and dedicated security professionals in the world in one of the most difficult threat environments faced by any technology company.”
'Stopping more malicious actors'
Stanford said Mr Stamos would join a new working group focusing on information warfare, designed to inform politicians, the media and others about new threats.
“We are thrilled that Alex is devoting even more energy to our cyber efforts,” said Amy Zegart, co-director of Stanford’s Center for International Security and Cooperation.
According to the New York Times, Facebook does not plan to appoint a successor.
In a statement, Facebook said: "Earlier this year we embedded our security engineers, analysts, investigators, and other specialists in the heart of our product and engineering teams.
"This has helped us do more to keep people safe, from detecting fake accounts in new ways, to stopping more malicious actors who manipulate people to spread falsehoods or share sensitive information."
Mr Stamos was criticised earlier this year when, in the wake of the Cambridge Analytica scandal, he lashed out at the media for describing the incident as a “breach”.
"I should have done a better job weighing in,” he later admitted, after deleting the tweets. Rumours of his departure emerged soon after.
Facebook’s Ms Sandberg on Wednesday praised Mr Stamos’ work.
“Alex has played an important role in how we approach security challenges and helped us build relationships with partners so we can better address the threats we face,” she said in an emailed statement.
"We know he will be an enormous asset to the team at Stanford and we look forward to collaborating with him in his new role."
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