Hi there, Administrator(s) of ozone3D.
I've found that there's a rather simple way of stopping spambots right at the registration screen. You'll want to make a custom field asking for something like "the sum of eight and nine", and from what I've found, none of the bots are the wiser. Pretty much all human beings online should have the capacity to pass a question like that, so you should be all set to go!
Hope that helps.