This plug-in is an excellent find!

Media file security has been a major useability issue on our site for several years. We’ve evaluated a number of possible solutions over the years that never met our needs until we found Prevent Direct Gold and its extension PDA Access Restriction. It took some work between the vendor and our hosting company to get the appropriate site configuration (issue with the way WordPress was set up by the host) and the BWPS support folks were excellent to work with through this. Now it does exactly what we hoped for, it will make a big difference to our users and it will make it much easier to fully protect our many media files. We think this plug-in is a real winner!