"Shamrock covered decades-old secret agreements with the nation's large telegraph companies under which NSA and its predecessor agencies automatically received

"Shamrock covered decades-old secret agreements with the nation's large telegraph companies under which NSA and its predecessor agencies automatically received copies of international telegrams. "At the peak of the operation, in the early 1970s, NSA analysts were reviewing 150,000 telegrams a month selected by computers scanning for keywords of interest to U.S. intelligence. Only in 1975, as Senator Church's committee began its inquiry, was Shamrock stopped."