Licensing deployed applications for copy protection

I recently stumbled upon the problem of licensing our application for copy protection etc. Our product will require yearly licensing and will also allow 30 day free trials. I want to make sure that users can simply copy the program over to another computer and that they have purchased the application. My application will contact licensing API when it is first registered, but I want the users to be able to work offline, so I need to store the licensing information somewhere on the computer and in a form users cannot tamper with it or simply copy it to another computer.

Has anyone any experience of this and if so, any suggestions on how to tackle this problem?

Regards

Craig