This isn't something new... In WW2, the Nazi army found out the US was listening in when two planes were flying in a DMZ, and a German Pilot decided to try a test out... He used a radio to call in for permission to fire on a pilot, at which point, the guy in the US plane, swerved, very quickly, out of the way. Basically, they found out that the US was listening in on their communications, by pretending to call in for permission to fire on a pilot, who responded to the request.

I always found that interesting lol.