It's a
TREMENDOUS add-on for any PHP based application, vBulletin included.

Since adding it to our forums in NOV, our Bandwidth usage has dropped due to fewer spambots being able to crawl the website any longer.(see log entries in above post)
On some days, unsavory spiders had pushed our BW usage up over 1gB/day, whereas normal (for us) was around 200-300mB/day. We were faced with having to
double our costs 
(i.e. by going to a larger hosting plan) when
ZB BLOCK helped us to curtail a lot of wasted bandwidth 'some' robots were chewing up for no good reason at all.
Visit
http://www.spambotsecurity.com/ for more info. :up: Highly Recommended!