I'm master, and when i challenge GM's to 1v1's on more then one occasion they were surprised i don't use map hack, because they do! thats just one example.
Its very hard to catch a map hacker by watching replays, and it does not mean they are good in any way what so ever, you can't hack better micro skills. Like i said I've played with map hackers and they are always at least diamonds, they'll be telling me what the enemy is building the whole time, how many unit they have, where they are on the map (no specific units, but where masses are) and yet they still can't produce the counter units to help me kill them. Nubs. I'd definitely say its 50%, its very hard to catch, and its not a full map hack it doesn't give you vision its like have a tower across the whole map from the way i perceive it to be. Actually ill just take a screen shot and show you what it looks like
