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Room 641A is a telecommunication interception facility operated byAT&T for the U.S.National Security Agency, as part of anAmerican mass surveillance program. The facility commenced operations in 2003, and its purpose was publicly revealed by AT&T technicianMark Klein in 2006.^[1][2]

Room 641A is located in theSBC Communications building at 611 Folsom Street,San Francisco, three floors of which were occupied byAT&T before SBC purchased AT&T.^[1] The room was referred to in internal AT&T documents as theSG3 [Study Group 3] Secure Room.

The room measures about 24 by 48 feet (7.3 by 14.6 m) and contains several racks of equipment, including aNarus STA 6400, a device designed to intercept and analyze Internet communications at very high speeds.^[1] It is fed byfiber optic lines frombeam splitters installed in fiber optic trunks carryingInternet backbone traffic.^[3] In the analysis of J. Scott Marcus, a formerCTO forGTE and a former adviser to theFederal Communications Commission, it has access to all Internet traffic that passes through the building, and therefore "the capability to enable surveillance and analysis of internet content on a massive scale, including both overseas and purely domestic traffic."^[4]

The existence of the room was revealed by former AT&T technicianMark Klein and was the subject of a 2006class action lawsuit by theElectronic Frontier Foundation against AT&T.^[5] Klein claims he was told that similarblack rooms are operated at other facilities around the country.^[6]

Room 641A and the controversies surrounding it were subjects of an episode ofFrontline,^[7] the current affairs documentary program onPBS. It was originally broadcast on May 15, 2007. It was also featured on PBS'sNOW on March 14, 2008. The room was also covered in the PBSNova episode "The Spy Factory".

TheElectronic Frontier Foundation (EFF) filed a class-action lawsuit,Hepting v. AT&T, against the company on January 31, 2006, accusing the telecommunication company of violating the law and the privacy of its customers by collaborating with theNational Security Agency (NSA) in a massive, illegal program towiretap anddata-mine Americans' communications. On July 20, 2006, a federal judge denied the government's and AT&T's motions to dismiss the case, chiefly on the ground of thestate secrets privilege, allowing the lawsuit to go forward. On August 15, 2007, the case was heard by theNinth Circuit Court of Appeals and was dismissed on December 29, 2011, based on aretroactive grant of immunity by Congress for telecommunications companies that cooperated with the government. The U.S. Supreme Court declined to hear the case.^[8]

A separate case filed by the Electronic Frontier Foundation was titledJewel v. NSA and was filed on September 18, 2008. After many years of litigation, on April 25, 2019, the ruling from the Northern District of California^[9] concluded that the evidence presented by the plaintiff's experts was insufficient: "the Court confirms its earlier finding that Klein cannot establish the content, function, or purpose of the secure room at the AT&T site based on his own independent knowledge." The ruling noted that "Klein can only speculate about what data were actually processed and by whom in the secure room and how and for what purpose, as he was never involved in its operation." The Court further went on to discredit other experts called upon, citing their heavy reliance on the Klein declaration.

In the spring of 2006, over 50 other lawsuits were filed against various telecommunications companies in response to the article.^[10] There has been speculation that several rooms similar to this exist all over the United States.^[11][12]

• 
  Page 17: Basic diagram of how the alleged wiretapping was accomplished. FromEFF court filings.^[4]
• 
  Page 9: More complicated diagram of how it allegedly worked. From EFF court filings.^[3]
• 
  A fiber optic tap

• 33 Thomas Street – Skyscraper in Manhattan, New York
• Cabinet noir – Type of government intelligence gathering office
• ECHELON – Signals intelligence collection and analysis network
• Fairview – Domestic spying partnership between AT&T and the NSA
• Fiber tapping – Extraction of a signal from an optical fiber
• Hemisphere Project – Mass surveillance program conducted by AT&T and paid for by the DEA
• Main Core – Alleged American government database
• NSA warrantless surveillance controversy – Part of Terrorist Surveillance ProgramPages displaying short descriptions of redirect targets
• President's Surveillance Program – Intelligence activities in the US
• PRISM – Mass surveillance program run by the NSA
• Signals intelligence – Intelligence-gathering by interception of signals
• Upstream collection – Term used by the National Security Agency
• Utah Data Center – NSA data storage facility

• "Electronic Frontier Foundation's web page about NSA's domestic spying".
• "Technician Mark Klein discussing Room 641A".Countdown episode. November 7, 2007. Archived from the original on March 10, 2016. RetrievedAugust 25, 2016 – viaYouTube.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
• Kris, David (2014)."On Bulk Collection of Tangible Things"(PDF).Journal of National Security Law & Policy.Archived from the original on October 27, 2017.

• AT&T buildings
• George W. Bush administration controversies
• History of cryptography
• Locations in the history of espionage
• National Security Agency facilities
• Privacy of telecommunications
• Signals intelligence
• Privacy in the United States
• Organizations based in San Francisco
• Individual rooms

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