[cicus]

When an opponent bids 2♦ then asks for undo and changes the bid to 2♥ it may have been because of a misclick. Mice can do that. However, if he changes it to e.g. double, it is clear that he only changed his mind. The problem is that I have already accepted the undo when I learn that the misclick was a lie.

I suggest an automatic procedure. If the opponent asks for an undo which is accepted, the software should deny the replacement of the bid if it is not next to the bid replaced. E.g. you could change 2♦ to 2♣ or 2♥ or 1♦ or 3♦, because these bids are neighbouring the initial one. Also, pass could be changed to double (or vice versa) but not to any other bid (it can't be a misclick because it needs two clicks instead of one).

Maybe the software could even tell the culprit that his undo was rejected automatically. A little pedagogical explanation may also be attached, e.g. 'this is no place for cheaters'.