Well, I've been getting attacked by spambots on a few of my sites and I've done something that seems to be working pretty well and thought I'd share. I didn't see any other posts talking about this, so...
I decided to rename ucp.php file across the whole site since it seems to be getting called directly by the bots that are attacking.
so, I renamed the file and then did a search/replace on "ucp." with the new filename. There were like 25 entries or something to fix, but no big deal.
The bots should just fail with a 404. I'm seeing a lbig increase in UCP.PHP 404 errors in the logs - which was expected, and no spambot accounts getting created. However, I did do the additional step of adding some custom registration fields just in case.
I thought I'd have problems on some pages after doing this, but I have not found a page that wont load yet. Obviously, when I go to upgrade to the next rev, I'll have to either re-do the mod or reverse it. but the change over was easy. It will only take 2 minutes to reverse it.