Block registration by IP address

[spamgirl]

Currently I have a long list of IP addresses, which happen to be dynamic, which I'd like to block from registering. The problem is they sometimes match the IPs of good members who are already on the forum. I'd like it so that people who can't register would contact me (as they have been so far) and I can check if they're a good member or one of the bad members.

Is there some sort of mod to add this functionality?

Thanks in advance!