I have installed many anti-spam plugins and made numbers of security measures to prevent this forum from spammer invasions and also to reduce moderating work for our unstoppable mods and me.
Last mod I have installed is "Spam-O-Matic" and I can tell you that it is working great , you can find it here(for VB 4.X):
[GlowHost] Spam-O-Matic - Spam Firewall stops forum spam - vBulletin.org Forum
This mod is using Stop Forum Spam database of SPAMMERS which is constantly updated.
That database is logging spammers from all over the world and from many different forums, membership, social and community sites as well as regular sites or any reported spammer by their service for that matter.
It logs, spammer IP, email amd username.
More mods/plug-ins for different type of websites that can use Stop Forum Spam database you can find here:
Stop Forum Spam - Mods & Plugins