The Electronic Frontier Foundation (EFF) recently announced the passing of Mark Klein, the AT&T whistleblower who exposed the NSA's mass surveillance program nearly two decades ago. Klein worked as a telecommunications technician at AT&T for 22 years when he discovered something alarming at the company's San Francisco facility: evidence of widespread government spying on American citizens.

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.