Multiple login single user should be restrict in C#.net

Question

I have deployed an windows application to my client,
wherein i need to restrict the user if he/she has logged in my application and is active.

Following validation is required:

1. If user is active and tries to open my windows application C#.net in a different PC i should pop-up a message box and intimate him that " He / She has already logged in" get the confirmation from he /she and then close the existing and allow the current one.

2. If not any other alternative to identify and the same.


Regards
RNS