Trial program expiry

What is the best way to make a 15-day demo?

Yes I've used the "search" button. But the codes that I found are not fool-proof.


My current method is to store the encrypted installation date in the registry. And whenever user opens the program, use the DateDiff function to see if it is over 15 days from the date of installation.


Apparently, that method has many holes.

1. I can change my comp date to something like "1/Jan/2337" before installing the program. After installaion, I change it back to year 2007. I will be able to use the demo program forever.

2. I can roll back to the installation date and keep using the demo forever..

How to prevent these?

Check in MartinLiss' signature for "A program registration scheme.

http://vbforums.com/member.php?u=3582

That is a completely different project..

Part of my program is based on his project "To get the serial key to activate the demo program"...


But now, I want to limit the duration of the license key...

Ok, you could add code to use the Inet control and connect to a time server to retrieve the real time. Then calculate the time left. etc.

I have given this some thought. Save the date in several places.
If the date saved is less then current date, add one to counter
Check a counter and compare, Like Rob suggested, use Inet.
Meaning, there are several ways: Date, Counter, Inet, other, combination of all.

The problem with storing the date is that the use could change the system data and try to fool the trial period. Using the internet time servers via inet only is half the issue. Like sessi4ml posted, saving the initial start date either in several locations or encrypting it would be even better.