Room 641A (AT&T surveillance room)

In 2006 former AT&T technician Mark Klein disclosed the existence of a secured telecommunications room known as Room 641A inside AT&T's San Francisco switching facility. Documents and sworn statements described equipment in that room used to copy and hand off internet and telephone traffic to the National Security Agency, prompting lawsuits and congressional attention. The room and related practices were central to public reporting and legal challenges about warrantless surveillance in the mid-2000s.