If the OS doesn't provide an 'out of the box' way to manage user permissions for that sort of access then you have a great deal of work ahead of you! On Windows most likely you would need to write your own filter driver and insert it into the driver stack for USB mass storage devices, but that would be more work than you want to think about and is not something you can do in Perl. I've no idea what is required in a *nix context, but I suspect Perl won't get you there in that context either.