The other posting do have valid points. 1) It will be easy to defeat protection in interperted languages. 2) Unless you spend a lot of time on the problem, it's not worth it.
If you really do need serious copy protection for your killer app, you should just purchase a pre-built solution from a vendor. You can find hardware key solutions from
Aladdin and
Rainbow Technology.
One final thought. All of these copy protection methods only attempt to make the cost of stealing the software much higher. There is no way to achieve perfect protection on the PC.
