Room 641A

A locked room in a San Francisco exchange where the internet forked into a splitter.

Imagine you're a telecom technician. You've spent decades splicing cables, reading wiring diagrams, keeping the internet's plumbing flowing. And one day you're handed the documents for a room you're not supposed to ask about. That's what happened to a man named Mark Klein. And what he found is DOCUMENTED — it's not a rumor, it's court evidence. Klein worked for AT&T in San Francisco, at the company's facility at 611 Folsom Street. Around 2002 and 2003, he became aware of a secret room on the sixth floor, labeled Room 641A. Ordinary AT&T technicians weren't allowed inside. Only personnel cleared by the NSA could enter. Here's what the room did, and this is the part that matters. The main fiber-optic lines carrying internet traffic ran through that building. Klein's documentation showed that AT&T had installed a device — a splitter cabinet — that took the light signals moving through those fibers and made a complete copy. One beam kept flowing to its destination. An identical duplicate beam was routed into Room 641A, into equipment including a Narus STA 6400, a machine built to sift and analyze enormous volumes of network traffic in real time. So here's where it gets serious. This wasn't a wiretap on one suspect's line. This was a copy of the backbone itself — the traffic of ordinary Americans, emails, web browsing, everything moving through that junction, duplicated and handed to the government. In 2006, Klein came forward. He turned over internal AT&T wiring documents to the Electronic Frontier Foundation, the EFF, a digital civil-liberties organization. The EFF used his evidence in a landmark lawsuit called Hepting v. AT&T, arguing the company had illegally helped the NSA surveil its customers. Now, the legal ending is documented too, and it's sobering. The case never got its full day in court. In 2008, Congress passed the FISA Amendments Act, which granted the telecom companies retroactive immunity for their cooperation. The courts ultimately dismissed the suit on those grounds. The evidence was real; the doorway to a verdict was closed by law. But Room 641A stands as one of the first concrete, physical, documented glimpses of domestic backbone surveillance. Not a leak of a slide deck — an actual room, with actual splitters, described by the technician who saw the paperwork. You should hold onto the distinction. Everything above is on the record: Klein, the room, the splitter, Narus, the EFF, the lawsuit, the immunity. What Room 641A ultimately fed into, and how it connected to the larger programs, is where documentation thins and inference begins. On the map, Room 641A sits shoulder to shoulder with its neighbors: it's widely seen as an early physical cousin of PRISM, the later collection program, and of ECHELON, the older global interception network. It's the moment the abstract became a room with a locked door.