Maintain Software Expiry date at client side

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C#

Hi friends,
i have a scenario.

i delivered my software to my client.I saved product activation date and product expiration date at my client's computer. now i want to add a counter to the Activation Date in client computer so that i can check it daily with the expiry date, make the product stop working.

keep these thing along with this.
1) counter must increase only once in a day, if he runs his product 5 time in a day, the counter must increase only once.

2) if he changes the the date of his computer to the back date, it should not effect the working.