[Invigilator]

I think "cheating" and "rule breaking" are not specific enough here. The word that comes to mind is unethical.

What multi-accounters are doing is unethical.

The existence of a penalty system in a sport addresses (seems to make the statement that...) doing certain things that are wrong, but not necessarily unethical. i.e. 5 for fighting in hockey, timeout for swearing at the WSOP.

"Underhanded" starts to touch on it. That which is concealed and unseen is an unethical effort. Emery boards being used by pitchers comes to mind.

Shifting the focus just to poker, multi-accounting, chip dumping, blah blah blah, all of these examples seem unethical, and worthy of severe penaly. (like poker sites sharing names of known multi-accounters. Yeh, that would be sweet).