Although this is not related to C::B, I`ll try directing you to an answer.
If I get your problem right, you need to ensure only one instance of your app is running on the target machine.
This is how it`s done.
Bear in mind though that this is not in any way a panacea, for sophicticated players may use additional PCs, virtual machines, diassemblers, and lots of other cool things to overcome the restriction you are trying to impose.