A bunch of us are fighting this same problem. This thread might be helpful:

http://forums.b2evolution.net/viewtopic.php?t=4512&highlight=bandwidth

The best option may be to use the script that generates a .htaccess file based on your antispam list (which you need to keep updated). The .htaccess file can block traffic before it eats up CPU and bandwidth.

Cool, thanks. I read through that thread and it does sound like I'm not alone. Unfortunately I'm lacking the knowledge that many of you you seem to have on this subject. Wat I did was uploaded http://isaacschlueter.com/tests/b2antispam_genhtaccess.php.txt to my admin folder and removed the .txt. I have no idea if that was the right thing to do, or if it's working. I also don't know how to update my antispam list, but I'd like to if you don't mind breaking it down for me or pointing me to a place where I can figure it out myself.

Big thanks for your help.

I'm still trying to figure out Isaac's htaccess script myself, so I won't be any help to you on that. To update your antispam blacklist, go to the backoffice, then the Antispam tab. Click on "Request update . . .". Repeat until it only returns one result. It will probably take several clicks to get all of the updates. Isaac has some instructions for getting the updates automatically:

http://isaacschlueter.com/blog/automatic_antispam_update_cron

That, combined with EdB's recheck hack has made my life a lot easier:

http://wonderwinds.com/hackblog.php/2005/02/07/antispam_recheck_tool_part3