Room 641A
loreprivacygovernance & risk
The San Francisco AT&T facility where a technician revealed fiber splitters copying Internet traffic for the NSA.
In 2006, retired AT&T technician Mark Klein disclosed documents describing a secure room at the Folsom Street switching center where beam splitters duplicated backbone fiber traffic into NSA-connected analysis equipment. The revelation fueled the EFF's Hepting v. AT&T lawsuit and, years before 2013's leaks, put bulk interception of domestic traffic on the public record. It remains the concrete image behind the phrase upstream collection.
Room 641A was a facility in an AT&T building in San Francisco, revealed in 2006 by a technician named Mark Klein, containing equipment that split fibre optic traffic and copied it. The documentation he provided indicated the copies went to a room accessible to the National Security Agency.
Its importance is evidentiary. Bulk collection had been alleged and denied, and this was physical infrastructure, installation records and a witness, describing a splitter on a backbone carrying ordinary domestic traffic. The subsequent litigation ran into state secrets doctrine and retroactive immunity for the carriers, which is itself part of the lesson about how such disclosures are absorbed.
Technically it is a clean illustration of why encryption at rest and in transit is not paranoia. A passive optical split is undetectable from either endpoint, costs the observed nothing, and collects everything that is not encrypted. The industry's response over the following decade, ubiquitous TLS, certificate transparency and encrypted transport by default, is directly traceable to the realization that the network path itself should be assumed hostile.