I have a site where I am going to be hosting a game which is free to play and users can win an iPad. Of course this is going to be very tempting for users to try and spoof so I want to get some ideas about how I can go about and prevent multiple accounts from being created from the same user. Of course some of the basics I already have covered are
Prevent multiple ip's
This is a basic to me which I already have covered, but I know this is easily spoofed from users assigning different ip's with hacks.
I have this covered where users cannot use the same username that has already been created
Covered. Can only use one email account per user
Besides these is there anything else I can do to tighten up security?