We're currently writing some software that we want to protect. We thought that registering a user's MAC address in a database upon activation of the software seemed viable; we can profile and grab that with a Java applet, (is there a better way?) so getting it isn't too much of a problem. However, we want their computer to only run the application, and download application files/updates from the server when their MAC address has been verified with their one on-file. We understand that this means a lockdown to one computer, but special changes can be made on request.

What would be the best way to verify their MAC address, to see if it exists in the database, and then serve them the files to run the application? (And to simply run it on subsequent requests, to prevent re-downloading.)