Since the leaks began, government officials have speculated about various NSA documents that former contractor Edward Snowden might have accessed. Today, that speculation reached a fever pitch, as unnamed officials told Reuters they now believe Snowden may have accessed the so-called "doomsday cache," which includes the names of US and allied intelligence personnel. The NSA takes great precaution to safeguard the data, with sophisticated encryption and multiple rotating passwords required to decrypt it, but officials say Chinese or Russian intelligence could be capable of decrypting the data under the right circumstances.
The officials expressed concern that Snowden had stored the information on a "data cloud," although this would be greatly out of step with what we know about his security practices before now, which have mostly relied on physical storage in multiple locations. It's also worth emphasizing that the anonymous US and British officials quoted by Reuters indicated no hard evidence that Snowden had taken the data, but merely that it was a concern within the agency, nor is it clear why they would have insight into Snowden's data storage practices.