In your documents-hptuners-settings folder you will find several files including your license.dat file which generate/regenerate anytime you connect/poll your interface.
This file keeps an account of all the vehicles you've licensed over the course of that interfaces life. The interface itself also stores that information but sometimes we use the license.dat as a backup in extreme cases.
HP Tuners recommends that you backup this file on a regular basis, weekly if you are a tunershop would probably be wise, monthly if you tune one or less vehicle a week and once a year if you just tune your own personal vehicle(s).
If you have any questions about this feel free to contact support.