Room 641A: The Secret Telecom Room That Could Turn Tapping Into a System

In 2006, technician Mark Klein gave the Electronic Frontier Foundation drawings he had seen while working at an AT&T facility in San Francisco. The drawings showed a specially guarded room wired to equipment that split traffic on the telecommunications network. The room was called Room 641A. Klein said the equipment in the room could send a copy of AT&T's traffic to the National Security Agency, the NSA.

The detail worth noting is where the room sat, not what it was called. AT&T was not a small office with a few phone lines. It was a large carrier that ran backbone routes. Data from very many customers passed through those routes before it went anywhere else. To watch people one by one, an agency has to find line after line. To reach many people at once, the agency only has to place equipment where the lines come together.