Wipe their score and disable their submission, but let them keep the account. I am aware they can still create a new account and start from scratch just as if we banned them altogether, but on principle I'd prefer to punish the offense itself, rather than the offender.
That message (it's not you we don't like, it's what you did) will probably be lost on most cheaters though. Oh well.
So I told the police: "Look, I know the DRILL. But don't BRACE yourselves just because I'm a dentist; I won't get on your NERVES, or BRUSH you off. I have FILLINGS too, you know. I CARIES for everyone and tell nothing but the TOOTH. That's why I'm the CROWN prince of dentists. I even received a PLAQUE for it. DENTURE wish your dentist was cool like me?". But they didn't buy it, so they performed a CAVITY search to EXTRACT a confession...