There is a critical security issue with the 2.0 version of the Akismet anti-spam plugin (which is bundled with most versions of WordPress), all users of this plugin should download the newest version of the plugin (2.02) from the Akismet download page and replace the files on their server. The newest version of WordPress 2.2 already has this latest version bundled with it, so upgrading to that version of WordPress will also close this security hole.