PerkZilla Fraud Center
IPs get entered in the Fraud Center based on flagging criteria.
Right now it's set for 2-3 users from the same IP as a low level, 4-5 as a medium and 6+ as a high suspicion.
You can then view these and manually unflag or blacklist the emails or full IP.
You can also add emails or IPs that you want to manually blacklist if needed. Blacklisting blocks the user from signing up from ANY of your campaigns.