Facebook Chief Information Security Officer Alex Stamos is reportedly leaving after disagreements over how the social media network should handle the spread of disinformation. The news was first reported by The New York Times, and later independently reported by Reuters and the Wall Street Journal.

In a tweet, Stamos said he was still employed, but that his role had changed to "exploring emerging security risks and working on election security."

Stamos tweet

The Times report said that Stamos's roles had been reassigned in December, but Facebook persuaded him to stay on until August.

Stamos has been a vocal advocate for investigating and disclosing Russian activity on Facebook and for increasing corporate responsibility in the tech world.

Stamos tweeted several times on Saturday, in the aftermath of the New York Times report detailing Cambridge Analytica's use of data gathered without Facebook users' permission. According to the account of a Cambridge Analytica whistle-blower, the company used this information to develop techniques that helped President Donald Trump's 2016 campaign.

@AlexStamos tweet

"There are a lot of big problems that the big tech companies need to be better at fixing. We have collectively been too optimistic about what we build and our impact on the world," he wrote on Twitter.

"I have always felt that the individuals who actually work on these problems should be engaged publicly. Doing so means balancing one's personal beliefs with their responsibility to their co-workers and employers. I don't know how to do that in this media environment," he added.

Current and former employees told the New York Times Stamos said he would leave the company back in December, but was persuaded to stay through August. Executives thought his departure might look bad.

Stamos would be the first high-ranking executive to leave the company since controversy broke out over fake news and disinformation on the site.

Facebook, already down nearly 7 percent during the day, fell another 1.5 percent after the bell.