It is quite easy to use software without authorization in Windows PCs. May be it will become a thing of past with Windows is going the mobile OS ways. Verifying the user (or at least the device) is not a problem in mobile apps.
In mobile platforms each device is identified with a user. That was not the case with PCs. Slowly this will change. But for the time being, we still have this problem.
How to check & restrict the software to run on only one PC (per license / account or whatever)?