Block external requests
Since version 2.8, WordPress allows you to define constants to control access to specific hosts from behind a proxy server.
It will block external requests from that time on. Though, some plugins need external request to work properly. If you experience problems, you can define a whitelist by pasting the code below into wp-config.php. Don’t forget to replace my url by the one needed by the plugin, and note that you should allow access to api.wordpress.org in order to ensure proper functionality of core files and plugins.