Klein, a former AT&T technician turned whistleblower, exposed mass surveillance by the U.S. government in 2006.

In 2006, he shared corporate documents showing how the National Security Agency was accessing internet data through a secret room in an AT&T office building.

Mark Klein, the AT&T technician who blew the whistle on one of the most extensive illegal surveillance operations in American history, has died. He was 79. He was an unlikely hero. For more than ...

TechCrunch · Image Credits:Mark Klein / Wikimedia Commons (opens in a new window) under a CC BY-SA 3.0 (opens in a new window) license. Mark Klein, a former AT&T technician turned whistleblower ...