Secure Files that were uploaded via the "Add Media" screen..

Hello,

I currently have a MU installation up and running. Users can upload documents (i.e Word, PDF etc. ) via the "Add Media" screen. When a file is uploaded, it is placed in a default directory based on the site id (i.e. "/wp-content/uploads/sites/40/2014/06/Doc2.pdf"). This means that the file is available to anyone with a link (i.e. "http://www.mysite.com/wp-content/uploads/sites/40/2014/06/Doc2.pdf").

Is there a recommended plugin that would "secure" these uploaded files so that only folks with certain roles who have logged in can access these files?

Any direction is appreciated.

Thanks!

Thanks