Clip: Season 2014 Episode 10 | 4m 3s
When an NSA agent showed up at AT&T headquarters, technician Mark Klein didn't think much of it. But later, he noticed a secret room — and uncovered an infrastructure suggesting that the government was copying all traffic going through AT&T's Internet backbone. FRONTLINE's "United States of Secrets: Privacy Lost" premieres Tuesday, May 20 at 10 p.m. on PBS.
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