I have a installation of Multisite that has a history of serious signup spam problems. When we ran WPMU 2.9.2 we tried this .htaccess method, this math plugin, and CAPTCHAs. After little success ...
We're running 3.1.1 multi-user with the latest BuddyPress plugin, but we're having all sorts of issues with splog signups. So far, we've started using Anti-Splog, Bad Behavior, ReCaptcha on the ...