AT&T provided NSA eavesdroppers with full access to its customers' phone calls, and shunted its customers' internet traffic to data-mining equipment installed in a secret room in its San Francisco switching center, according to a former AT&T worker cooperating in the Electronic Frontier Foundation's lawsuit against the company.

According to a statement released by Klein's attorney, an NSA agent showed up at the San Francisco switching center in 2002 to interview a management-level technician for a special job. In January 2003, Klein observed a new room being built adjacent to the room housing AT&T's #4ESS switching equipment, which is responsible for routing long distance and international calls.

"While doing my job, I learned that fiber optic cables from the secret room were tapping into the Worldnet (AT&T's internet service) circuits by splitting off a portion of the light signal," Klein wrote.

The split circuits included traffic from peering links connecting to other internet backbone providers, meaning that AT&T was also diverting traffic routed from its network to or from other domestic and international providers, according to Klein's statement.

The secret room also included data-mining equipment called a Narus STA 6400, "known to be used particularly by government intelligence agencies because of its ability to sift through large amounts of data looking for preprogrammed targets," according to Klein's statement.