"Licence" an excel spreadsheet

Hi all

My specific question is:

I have a spreadsheet that I have developed specifically to help with different bank criteria and the processing of loan applications for my role as a mortgage broker. How can I set this up so that if I let someone use my spreadsheet on their pc that it can't be distributed and used by other people?


Further background:

The spreadsheet, to be fair, is not that complicated, and I am sure basic by a more experienced persons standards. But it takes into account the tax rates, investment loans, rates and payments for a range of banks and has taken time for me to produce. So if people are going to want it then I would rather protect my time and interests with a license or something?
Could I put in a hidden formula that links to a file stored locally to identify preferred users laptops??

I am interested in learning more about making the spreadsheet more advanced perhaps, but don't really know where to begin to learn how to do so.

Any ideas would be great on how to advance my skills or the protection of the work done, thanks.


Vim