Dan203 It totally depends on what information your software combines to create a "machine ID" since there is no such standard thing in Windows. A common value that is used is the GUID at Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography and I found this to be the stable over time in Sandbox from run to run. This is one of those cases where rolling your own is probably not worth the trouble, just license some proven licensing scheme and use it. You seemed surprised at the concept that Sandbox would allow someone to use your trial over and over, but if that were true then any Virtual Machine could have been used to do the same thing up to now (even better since with a virtual machine you can install all the stuff you need once and then refresh the VM only when your trial runs out. In other words this problem might be new to you, but it's not new at all. Good luck.