It is reported that the US underestimated the ability of the Chinese to penetrate the communication system used by the CIA to interact with its sources in China, having previously deployed the same system successfully in the Middle East.
According to an article by Zach Dorfman in ForeignPolicy.com five current and former US intelligence officials are now blaming this failure for China’s ability to dismantle the CIA’s Chinese agent network over two years from late 2010, executing dozens of suspects.
China’s alleged recruitment of former CIA officer Jerry Chun Shing Lee is also believed to have contributed, but penetration of the communication system is described as accounting for the speed and accuracy of the operation. One of the US officials is quoted as telling FP: "The attitude was that we’ve got this, we’re untouchable," another adding, "You could tell the Chinese weren’t guessing. The Ministry of State Security [which handles both foreign intelligence and domestic security] were always pulling in the right people."
All the CIA assets detained by Chinese intelligence around this time - variously put at a couple of dozen to more than 30 - were eventually killed, the former officials said.