If your contestant signs up multiple times from the same IP address, they will automatically be marked as a cheater.
However, there are more indicators that a user is a cheater than just their IP address signup.
To check their cheater score, we recommend you analyze the user under the Winners & Contestants tab:
Then either search a user by their email address, or click on the link that says "Analyze User Profile."
On this page you can see their cheater score, which indicates the likelihood that the user cheated on your contest. The higher the cheater score, the more likely they cheated.
We recommend marking users who have a cheater score over 70 as a cheater.