<<Rogue transmissions on ATC frequencies are immediately countermanded by the person who knows it is a rogue transmission. (i.e. the person who is being impersonated, whether pilot or ATC.)>>
An interesting statement. It happened to me and I never heard the person on the ground because he was out of range of our receivers. All I knew was an aircraft suddenly read back a speed reduction which I had not given. It resulted in a loss of separation and I don't believe they located the "pirate controller". Sadly, this sort of thing happens... because anyone can buy an air band transceiver, no questions asked..