Excel VBA macro to allow using an Excel file only if user possess a licence code

Closed - This job posting has been filled.

Job Description

One of our application (Excel Workbook with macros in VBA) has to be distributed to more user, the customer bought a fixed number of licences and we need to be sure that only the PC of licensed user will be able to run this app.

Please note: i don't need a complicated supersecure licensing solution (I trusts those guys), just something "quick and dirty" and low cost to help us not loose control of the matter.

To keep things simple I was thinking about something like:
- when user opens the file a sheet is shown asking for licence code
- if user don't have the code everything else in the workbook is hidden
- user enters the code and unlock the file
- code is recorded so next time he can open directly the file

I accept any suggestion on the algorithm: code can be based on requester email, PC information... don't know. I'm looking for someone expert on this.
If user has necessary skill to help us even in figuring out how this should work it will be appreciated.

If somebody has alredy developed something similar we are available to adopt the solution either

Please provide an effort estimation in hours or a bid. We are open to both job types.