If you want a sure-fire way to make sure there are no “extra” administrator accounts registered in your blog, I suggest going straight to the source: your MySQL database. The following SQL query, run against your WordPress database will show you all users who have the Administrator role:
SELECT u.ID, u.user_login
FROM wp_users u, wp_usermeta um
WHERE u.ID = um.user_id
AND um.meta_key = 'wp_capabilities'
AND um.meta_value LIKE '%administrator%';
Advanced users can run this directly in the command-line MySQL client, or you can do it from phpMyAdmin by selecting your WordPress database and then going to the ‘SQL’ tab to run the query. If you use something other than the standard ‘
wp_‘ prefix for your table names, make the appropriate change in the query (three occurrences).