If your WordPress site doesn’t have protection from spam, then I guarantee you that you’re spending too much time sifting through spam comments and deleting spam registration accounts from your site. Spam is a common problem for WordPress sites, because bots have been trained to find vulnerable sites running on WordPress.
Block by Math Reloaded is a new plugin that was based on the Block-Spam-By-Math plugin created by Alexander Grau. It adds a simple math question to spam-vulnerable areas on your site. This new plugin is primed to work with WordPress 3.0. Check out a screenshot: