There are, however, serious security violations on the air from time to time. Not, of course, only on military frequencies...
My own tale, from a friend:
FBI/NIS working a surveillance in the motel his family is managing, borrowing a room. He's there, chatting, has his own scanner with him, yes, monitoring NIS. Suddenly from the NIS channel comes a unit up at Miramar NAS (This was long ago, folks), investigating an alarm at the nuclear weapons bunker. (Security Violation 1, they don't officially admit there ARE nuclear weapons there).
He's there, he's forgotten his little book of info, talking to the base station at Miramar. Asks for the alarm disarm code to said bunker door. They give it to him, yes, in clear, open channel. (Security Violation 2) Also asks for, and gets, lock code. (And it's the triple, for the win!)
NIS and FBI, back at the surveillance, look at each other. 'I didn't hear what I think I did, did I?' 'Yes, yes, you did!' Friend is nodding to them. Many sighs. They phone Miramar NIS and Base Commander, to start up the required investigation for such major security breaches. Expect some idiot got to visit a new duty post with less than nice conditions.