Securing a WordPress 3.0 site
Ensure you have the most recent version
Upgrading to the version 3.0 (as of the date of this article) will address many security vulnerabilities, including the protection of your wp-content/plugins directory, and your wp-admin folder. These directories in 2.x versions had security issues and as such were prime targets for attacks. Also be sure to upgrade all of your plug-ins, where applicable. Regardless of how many WordPress sites you may be running, or how hard it may be to upgrade 10’s or 100’s of them, it’s better than having all of their content deleted and thus having to do reinstallations anyway.