It's for a competition where surfers vote for the winner and the prize may have monetary value thus an incentive to cheat. Hardware diagnostics sounds neat but I've got no idea how to do it. Seems in this case there is only no ways to do it. As suggested I'm going to try to use a combination of cookies, sessions and IP but for now failing that we may have to do it for fun instead of prizes. Unfortunately I can't add a step for random number validation or registration but I'll keep them in mind for the future. I'm sure the online raffle they want next will cause me even more problems :(
thanks anyways