I am interested in a password system for my lease computers. I would like to be able to preprogram 12 passwords into the computer when I lease it out. Every 3 months, the computer would require the next password to continue operating. I would then supply the customer with the password for the next 3 months. This would allow me to have some control over non paying customers. The program would have to be such that they couldn't simply change the computer date, or reformat the hard drive to defeat it.
Complete and fully-functional working program(s) in executable form as well as complete source code of all work done.