Watch out for suspicious job offers on LinkedIn. Chinese government agencies are using the social network to recruit Americans for spying purposes, a US spy chief says.

According to William Evanina, director of the National Counterintelligence and Security Center, China is contacting "thousands" of LinkedIn members in a bid to uncover US government and commercial secrets.

Linkedin "makes for a great venue for foreign adversaries to target not only individuals in the government, formers, former CIA folks, but academics, scientists, engineers, anything they want. It's the ultimate playground for collection," Evanina told Reuters.

China has been using LinkedIn to reach out to experts in supercomputing, nuclear energy, nanotechnology, semiconductors and other tech fields, according to Reuters, citing unnamed US officials. Although Russia, Iran, and North Korea also exploit LinkedIn for recruiting purposes, China is viewed as the most prolific and will use tactics such as bribery and phony business deals to lure in potential informants.

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Evanina stopped short of saying whether he was frustrated by LinkedIn's response to the spying activities. However, he did urge the Microsoft-owned platform to take a page from Twitter, which deleted millions of suspected fake accounts.

Earlier this month, LinkedIn announced it had ousted a group of fewer than 40 fake accounts that tried to connect with members of US political organizations. However, it isn't clear who was behind those fake accounts or what their intentions were.

In response to Evanina's reported comments, LinkedIn said: "We've never waited for requests to act and actively identify bad actors and remove bad accounts using information we uncover and intelligence from a variety of sources including government agencies."

The company also has a "threat intelligence team" specifically devoted to stopping malicious activities. But LinkedIn refrained from directly commenting on suspected Chinese government espionage campaigns or how many fake accounts might be involved.

Evanina is speaking out about LinkedIn after a former CIA officer was convicted in June of spying for China. The officer, Kevin Mallory, became embroiled in the espionage campaign after he received a message over LinkedIn in February 2017 from a Chinese headhunter. Mallory now faces life in prison for handing over US secret documents to a Shanghai think tank with alleged ties to a Chinese security ministry.

This article originally appeared on PCMag.com.