In case you missed it (though I'm not sure how you would) there was a scare for WordPress users out there that have been using an older version of the popular blogging engine about a worm going around an exploiting a hole to create a user, become an admin and quietly put spam links and malware into your posts without you knowing. The solution? Simple! Update right away!.
If you're currently running an older version of the WordPress software and want to be sure that you haven't fallen prey to the worm's threat, you can use the query Dougal Campbell has posted to check your wp_users table for administrators. Check the results of this to make sure there's no extra admin accounts found.
Keeping your software up to date is always a good first line of defense, so be sure that you've downloaded the latest to keep you and your blog protected.