The Criminals Thought the Devices Were Secure. But the Seller Was the F.B.I.

Global law enforcement officials revealed a three-year operation in which they said they had intercepted over 20 million messages. Hundreds of arrests were made in more than a dozen countries.

MELBOURNE, Australia — The cellphones, procured on the black market, performed a single function hidden behind a calculator app: sending encrypted messages and photos. For years, organized crime figures around the globe relied on the devices to orchestrate international drug shipments, coordinate the trafficking of arms and explosives, and discuss contract killings, law enforcement officials said. Users trusted the devices’ security so much that they often laid out their plans not in code, but in plain language, mentioning specific smuggling vessels and drop-off points. Unbeknown to them, however, the entire network was actually a sophisticated sting run by the F.B.I., in coordination with the Australian police.