150 agents were to be assigned. All it had discovered was the history of the preparations for a major espionage revival. It now knew that the SVR had installed plumbing in America that one or more agents in this network had been activated to handle a possible recruit in the NSA. But without anyone left in the sleeper network to follow and without an inside source in the SVR, it had no further avenues to fruitfully pursue. The revelation of the sleeper agents had little, if any, other intelligence value. The NSA’s own security investigation turned up no evidence of a leak at Fort Meade in 2010. The absence of evidence of a penetration in a security investigation is not in itself evidence of the absence of a penetration. The Russian intelligence service had demonstrated in the past it was well-schooled in covering its tracks in operations against US communications intelligence. For example, CIA counterintelligence had learned from a KGB defector in the early 1960s that Russian intelligence had penetrated the cipher room at the US Embassy in Moscow and, because of this operation, the KGB was able to decipher crucial communications. Even so, it failed to find either the perpetrator or any evidence of his existence for more than a half century. The operation was only definitively revealed by Russian spymaster Sergey Kondrashev in 2007. Tennent Bagley, who headed the CIA’s Soviet Bloc counterintelligence at the time, late wrote in his book that the ability of Russian intelligence to conceal this penetration for more than a half century “broke the record for secret keeping.” This Russian ability to penetrate US intelligence was not entirely defeated by America’s implementation of more sophisticated security procedures, such as the polygraph examination and extensive background checks. In 1995, only 10 years before Snowden joined it, the CIA's inspector general completed a study of the KGB’s use of false defectors to mislead the US government from the end of the Cold War