Washington Post Explains How It Knows NSA Accessed Google, Yahoo Data

In response to NSA criticism of reporting

The Washington Post reported last Wednesday that the National Security Agency has been tapping into the private links that connect Google and Yahoo data centers around the world. Today we offer additional background, with new evidence from the source documents and interviews with confidential sources, demonstrating that the NSA accessed data traveling between those centers.

The background also helps explain the response of U.S. officials following the publication of the story.

The U.S. government declined repeated requests to discuss the story beginning eight days before it was published. Since publication it has made four responses.

Immediately after the story posted online, a reporter asked NSA Director Keith B. Alexander about it at a cybersecurity event hosted by Bloomberg Government. Neither the reporter nor Alexander had read the story yet.

General, we're getting some news that's crossing right now being reported in The Washington Post that there are new Snowden allegations that say the NSA broke into Yahoo and Google's databases worldwide, that they infiltrated these databases?

Alexander replied:

That's never happened. […] This is not the NSA breaking into any databases. It would be illegal for us to do that. And so I don't know what the report is, but I can tell you factually we do not have access to Google servers, Yahoo servers.

The story did not say the NSA breaks into "servers" or "databases." It said the agency, working with its British counterpart, intercepts communications that run on private circuits between the fortress-like data centers that each company operates on multiple continents.