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Your account gets banned - that means all of your sites AND you as a person get banned. Also, anyone associated with you. How they define associated seems to allow them flexibity, but clearly they really mean to crack down hard on anyone that gets booted.
I don't know how likely it is that ad networks share blacklists like credit agencies here do, but if I were Yahoo or whoever I'd be very keen to know if new sign-ups have been ejected from other programs. I'd imagine they are trying to find out this info - or at least that's what I'd be doing if I were them.