I know many of you have forums. I have had the problem with my Vbulletin forums in the last few weeks of getting massive new sign-ups all posting spam.
These are all done automatically by spam bots. These spam bots are even so smart they bypass the captcha.
With that said I implemented a simple solution on the registration page that takes care of all the bots.
There is a mod called "Nospam!" found on vbulletin.org. Works like a charm and takes a few seconds to set up. I highly reccomend it to anyone else dealing with increased spam on VB forums lately.