Real users don't have the option to input anything in their website and signature fields when they sign up. Sufficiently dumb bots won't realize the registration form has been altered to prevent it, and when they try to submit that data their registration just gets ignored. Since the mod that implemented this has no way to track how many registrations have been stopped by this I don't know how effective this has been.
As far as I can tell it's impossible to ban a whole TLD like .ru, though I would love to ban all of .ru and all of .info, phpBB won't accept *@*.ru or simply *.ru as a valid argument for banning by email address.
I have a few other tricks in place, but it's getting to the point where the bots are catching on and I don't have the resources to be adding more and more anti-spam mods every couple of months (or even weeks!) to keep up. Hopefully some of the changes with the upcoming new forums will help (a new URL, and a new board type, SMF, which comes with better user management, for example.)
