I have started blocking the ip address for all the spamers, this should prevent them being able to re-register once they have been blocked.
Don't really know to much about where they come from or why they do it.
I noticed you call them bots, is this because this stuff is posted electronically?
As with many sites you have to enter a code from an image before you can register, but this does not seem to do much to prevent them.
Ever since this site started showing up in google they been increasing in number every day, I have also seen forums that have been completely overrun with it, while at the moment it is manageable here I worry to what extent it may reach.