In addition to the stopforumspam mod that 1af mentioned, I've recently ran across another similar database/mod. I had been monitoring the user of this post
and on an off chance googled his email.
Turns out he is a recgonized and registered bot with the BotScout project
. I'm guessing the account is registered here as a sleeper bot.
There's a few different ways that BotScout can be used, and they do have an SMF plugin. BotScout can be used at registration time to automatically block known offenders, or it can traverse over a list of existing users to detect bots that have previously registered.