I want to provide a trial version of my software. This version should only be evaluated within a specific period of time. Let's say only during January 2011.

As this software massively uses the system clock in processing, it would be quite annoying to set the clock to an earlier time to be able to use it over and over. So because of this, I wound't think of a more complicated protection mechanism.

So I have thought about exiting after a test like:

if (DateTime.Now.Year != 2011 && DateTime.Now.Month != 1)
{
    MessageBox.Show("expired!");
    Application.Exit();
}

How easy will this be cracked :-) ?

Is there a "safe" way to do this ?