I've a simple product installer for windows OS, which could be evaluated for a month. What are the techniques I can use so that this piece of software is not used after a month? I've seen that several s/w use system date to check it but it's very primitive and easily forge-able. I think a key based system based on registry or online verification could be an option but I don't know much about these.
Please help.
EDIT
I found this thread helpful.