US Senate Select Committee On Intelligence is investigating why developers in Russia, China, Iran and North Korea had access to Facebook user data.

Senators Mark Warner and Marco Rubio, chair and vice chair of Committee on Intelligence, wrote to Facebook parent Meta Platforms META.O on Monday about documents that show it knew developers in China and Russia and Iran had access to user data that they could use for espionage.

"It appears from these documents that Facebook has known, since at least September 2018, that hundreds of thousands of developers in countries Facebook characterized as 'high-risk,' including the People’s Republic of China, had access to significant amounts of sensitive user data," Warner, a Democrat, and Republican Rubio wrote in the letter to company founder Mark Zuckerberg.

The letter said an internal Meta document showed that nearly 90,000 developers in China had been given access to information about users, including profile data, photos and private messages even though Facebook had never been able to operate in China.

More than 42,000 developers in Russia and thousands in Iran and North Korea also had access to the information, they wrote.

The unsealed documents came to light as part of litigation in the Northern District of California that was filed in 2018.

"We have grave concerns about the extent to which this access could have enabled foreign intelligence service activity, ranging from foreign malign influence to targeting and counter-intelligence," the two senators wrote.

Facebook did not immediately respond to a Reuter’s request for comment.

Reporting by Reuters