US and West German intelligence agencies spied on governments across the world for decades using a Swiss encryption firm, a new investigation has claimed.
Hundreds of countries used Crypto AG equipment to protect their top secrets but a probe has found the firm was covertly owned by the CIA and German spy agency BND.
But, by rigging the equipment, American and Western German intelligence agents were able to listen in on their allies and enemies.
The revelation came from a classified CIA report that was obtained by German public broadcaster ZDF. It worked with the Washington Post to break the story.
ZDF's Washington bureau chief Elmar Theveßen told Euronews it was likely the "biggest intelligence eavesdropping operation of the past 60 years".
He said US and West German intelligence agencies used the programme from 1970 to 1993, with the CIA continuing alone until around 2018.
Theveßen said it was used, for example, to listen in to what was happening during Argentina's military dictatorship in the 1970s.
"The US and Germany were able to basically know everything about what was going on with regards to critics of the regime," he said.
"More than 30,000 people were killed back then. They just disappeared and Germany and the US knew exactly what happened through listening in to these communications and, of course, this prompts the big ethical question: why didn't they do anything about it?"
Theveßen also claimed intelligence agencies shared information with then UK Prime Minister Margaret Thatcher that could have prevented the Falklands War.
Watch the full interview with Elmar Theveßen in the video player above.