NSA fears Snowden saw details of China spying.

The National Security Agency is worried that Edward Snowden may have accessed files that reveal how the United States spies on China and other strategic countries, The Washington Post reported Thursday.
An internal review has found that the former NSA contractor "was able to range across hundreds of thousands of pages of documents," the Post wrote, citing an unidentified former official briefed on the issue. But another intelligence official, also unidentified, told the Post that so far it did not appear that Snowden obtained data collected through hacking or other means.
The official said Snowden had "got a lot" but "not even close to the lion's share" of the NSA's intelligence trove. Nonetheless, the official described potential harm to U.S. surveillance efforts as "a concern."
The Post writes:

The possibility that intelligence about foreign targets might be made public has stirred anxiety about the potential to compromise the agency's overseas collection efforts. U.S. officials fear that further revelations could disclose specific intelligence-gathering methods or enable foreign governments to deduce their own vulnerabilities.

Snowden has stated publicly he does not plan to publicize technical specifics of the NSA's operations. He has archived encrypted documents with others, the Guardian newspaper has said, and U.S. officials worry they could eventually be out of his control.
The Guardian's Glenn Greenwald told the Daily Beast that "if anything happens" to Snowden, "the stories will inevitably be published."
Snowden leaked the files to the Post and the Guardian.
Separately, Greenwald and other Guardian reporters wrote that documents leaked by Snowden show that Microsoft "collaborated closely with U.S. intelligence services to allow users' communications to be intercepted." The company said it was legally obligated to cooperate.
With Microsoft's help, the NSA evaded encryption to intercept e-mails on Outlook and Hotmail, and Web chats and video calls on Outlook and Skype. It also gained access to SkyDrive, the company's cloud storage service.
The NSA shared the material with the FBI and CIA,the Guardian said. One agency document described the effort as a "team sport.."
The formerly secret files illuminate the workings of the PRISM surveillance operation and reveal the extent of cooperation between big technology companies and the government during the past three years, the Guardian said.
Microsoft responded that it merely follows the law.