Since World War I, countries around the world have been broadcasting mysterious numerical messages via shortwave radio. Though concrete evidence is hard to come by, the general consensus is that these coded messages are meant for undercover agents operating abroad. And one particular Russian station may have an even more sinister purpose. Featuring computer engineer Andrus Aaslaid, historian Maris Goldmanis, and documentary photographer Lewis Bush.

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To dive deeper into numbers stations, visit numbers-stations.com and priyom.org, or check out Lewis’ book, Shadows of the State.

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