Hi, this is my first post, please bear with me If I've made any mistake.

I'm currenly creating a win form with c sharp (1.1). I was wondering how can I make a "trial" version so that the program can only be used for, let's say, 30 days after installation.

I was thinking of using the datetime object to record the installation date, but then what if the client change the system date after the installation? I noticed that those trial software we got from the internet will indeed stop functioning after certain amount of days, regardless of how we modify our system date. I wonder how they did it ?

I've been googling for this but couldn't find any solution. Please clue me on this. Thanks...