I think it's government propaganda. The only foreign espionage stuff I remember hearing about was this[1], which turned out to be a false flag leak[2] (!!!).
Downvote away, but this has come up repeatedly and no one has managed to provide a source. Meanwhile the fake incident I just linked is strong evidence that the government is willing to go to lengths to construct that narrative. It's been repeated so often that even Snowden supporters are starting to leave it unchallenged, but I think we're witnessing revisionism right here. In fact, as far as I can tell Greenwald et al have exercised considerable restraint in only publishing activities with bearing on domestic surveillance.