Unzip the zip archive and upload the htaccess-secure-files directory to your /wp-content/plugins/ directory.
Activate the plugin through the 'Plugins' menu in WordPress.
On the 'Settings' -> 'Secure Files' admin screen select which roles, capabilities, and IP addresses will be allowed to access secure files and what the server response should be for those denied access.
To secure individual files edit the file on the 'Media' admin screen and change the 'Secured File' setting to 'Yes'.
Requires: 3.2.1 or higher Compatible up to: 3.3.2 Last Updated: 2012-6-8 Downloads: 4,195