Su The Economist, un articolo sui metodi di comunicazione dei servizi segreti (€ — alt).

Priyom.org, a website which tracks “number stations” used during Cold War by spy agencies to communicate with agents in the field, notes that activity has “significantly increased” since the mid-2010s, with broadcasts in voice, Morse code and digital signals. Russia is still a particularly keen user. With all the new technologies available, why use radio broadcasts?