We use Spam-O-Matic and Botscout.
Spam-O-Matic -
https://vborg.vbsupport.ru/showthread.php?t=248042
Botscout -
http://www.botscout.com/
We use to use vbstopforumspam but upgraded to spam-o-matic for it uses more engines.
Spambot requires you upload 1 file into the includes folder and adding 1 line of code into the register.php file. We get on average 300 bots attempting to sign up daily and all blocked.
Thanks,
DBC-Forum.net Webmaster