Former AT&T engineer Mark Klein has become a whistleblower who exposed mass surveillance by the US government, but died at the age of 79.
Klein was released in 2006 and revealed that the NSA is using the secret room at San Francisco's AT&T hub to use the internet backbone.
Behind the doors of the now-now-famous Room 641A, optical splitting eavesdropped on the same copy of raw internet traffic and returned to the NSA.
Klein's disclosure used powers granted by Congress in the aftermath of the September 11, 2001 terrorist attacks to confirm that the US government has access to internet data about millions of Americans.
In 2013, then-NTSA contractor Edward Snowden leaked thousands of confidential documents to journalists detailing wide-scale NSA surveillance around the world.
Klein's death was confirmed by the Electronic Frontier Foundation, a San Francisco-based digital rights group that Klein looked at, and continued to sues the federal government following Klein's disclosure. The case was ultimately dismissed.