Room 641A

Room 641A is a classified facility located within AT&T's Folsom Street telecommunications building in San Francisco, California, that was exposed to public attention in 2006 by former AT&T technician Mark Klein. Klein revealed that the room housed National Security Agency equipment designed to intercept and copy internet and telephone communications passing through AT&T's network infrastructure.

According to Klein's technical documentation and sworn testimony, Room 641A was constructed in 2003 as part of a secret arrangement between AT&T and the NSA. The room contained sophisticated signal processing equipment, including a Narus STA 6400 traffic analyzer, capable of conducting real-time surveillance of internet traffic, email communications, and telephone calls passing through AT&T's network backbone.

Klein's revelations included technical drawings and equipment specifications showing how fiber optic cables carrying internet traffic were split, with copies of all data being diverted to the secret NSA facility. This arrangement allowed the intelligence agency to conduct mass surveillance of domestic and international communications without obtaining individual warrants, raising significant constitutional and privacy concerns.

The existence of Room 641A became a cornerstone of the Electronic Frontier Foundation's lawsuit against AT&T, challenging the legality of warrantless mass surveillance programs. Klein's evidence provided concrete proof of the technical infrastructure supporting domestic surveillance operations that had previously been the subject of speculation and denial by government officials.

The Room 641A revelations contributed to broader public understanding of NSA domestic surveillance capabilities and helped establish the factual foundation for subsequent disclosures about government surveillance programs. The case demonstrated the crucial role that corporate cooperation plays in enabling mass surveillance and highlighted the constitutional issues surrounding warrantless interception of American citizens' communications.

While the specific equipment and operations in Room 641A may have evolved since Klein's 2006 disclosures, the facility remains a symbol of the technical infrastructure supporting domestic surveillance programs and the importance of whistleblower revelations in maintaining democratic oversight of intelligence activities.