If you’re a WordPress user and have a problem with comment spam you need to get the Link Right 2 Spam Plugin. Here’s how it works, which is actually very simple:
A simple WordPress 1.5 plugin that virtually eliminates comment spam. Prevents blind posting by adding a dynamic hidden field to the form and validating that field when posted. By default it logs all pertinent information to error_log so you can track the type and frequency of spam.
Since installing this plugin a couple months ago I have had zero spam comments! You can still spam my blog, but you’d have to be a human being until, and until they change the spam bots, that’s entirely too inefficient.