From foreignpolicy.com
Around 2013, U.S. intelligence began noticing an alarming pattern: Undercover CIA personnel, flying into countries in Africa and Europe for sensitive work, were being rapidly and successfully identified by Chinese intelligence, according to three former U.S. officials. The surveillance by Chinese operatives began in some cases as soon as the CIA officers had cleared passport control. Sometimes, the surveillance was so overt that U.S. intelligence officials speculated that the Chinese wanted the U.S. side to know they had identified the CIA operatives, disrupting their missions; other times, however, it was much more subtle and only detected through U.S. spy agencies’ own sophisticated technical countersurveillance capabilities.