[Plugin: Restricted Site Access] Blocking both site.com and www.site.com

Correct me if I’m wrong, but this plugin will only block whatever version of the domain is setup in WP, correct?

I have sitename.com as the main url in WordPress and this plugin blocks that fine but what about if I went to http://www.sitename.com? That version of the site with the www is still unprotected. How could I block both?

http://wordpress.org/extend/plugins/restricted-site-access/