Make sure you require email verification... here are two hacks that will help:
Spam Decimator
https://vborg.vbsupport.ru/showthread.php?t=93762
Allows you to click 'Spam' on a post to delete the users posts and ban his account. It also shows you other users with the same IP.
Prevent Spam Posts
https://vborg.vbsupport.ru/showthread.php?t=131568
Lets you enter keywords which when encountered in a post will set the post as awaiting moderation. It will only affect users with X or less posts.