Thanks for your replies so far. I should tell you a bit about what I'm trying to do. I have written an ASP script that lists files/folders. I want to encrypt the script so when I sell the script, they can't see the source-code (it'll be encrypted). I need some way of stopping them from just copying the ASP files to any computer they wanted. So I thought if I generated a serial number based on some ID from the server/computer, that they would then not be just able to copy it from server to server. If they wanted to copy the script to another server, they would have to request another serial number. I know there's probably a lot of holes in doing it this way, but I've never had any experience selling any of my scripts. Regards, Craig.