I have a bunch of anti spam solutions installed in my sites, but I still keep getting spammer registrations. I have a site where I want people to register on the blog, but they don’t usually make comments. Spammers keep registering. The spam software keeps them from commenting, but I have to go through and clean up the registrations every few days.
I made the Stop Spammer Registrations Plugin to check email addresses against the StopForumSpam.com database. In the first hour after I installed it, it stopped 5 registrations. It also prevents comments where the spammer puts in his email.
It is dead simple, just hooking the email validation routine and returning false if the email is bad. I log the last 20 bad emails.