ZigTrap adds a honey trap to your comments form.
ZigTrap adds a hidden field to your comments form, which humans will leave empty because they don't know it's there. Spam bots, however, will normally enter some content in it, and this springs the trap, causing WordPress to show a message and not save the comment at all.
Use this in conjunction with Akismet for a pretty solid spam prevention package.
Please ensure that the comments form in your theme calls the 'comment_form' action.
For further information and support, please visit the ZigTrap home page.