I have banned both spammers, but I don't want any more spammers being able to jump on..

I need help because I've already had two of my first users be spammers (the forums for a MC server I run) and I would like to know if there is any way that I can get a good set of software to stop them!

Thanks!

Website:
-http://zoritec.x10.mx/forums/index.php