Hello! I'm still thinking about the best way to prevent this from happening.
First I thought that checking the IP address would be fine, but this would work only for people with static IP. Also, they could register more than once using a VPS, proxys, etc.
So now I'm thinking that every member should get a unique code which can be used to register. They would need to submit a google form with their Bitcontalk profile, and the account must be an active one registered before the 1st of September. Once I check this, they would get the code. This is more time consuming, but it will be fair for everyone.
If anyone has any suggestion please tell me!