I sell an Excel worksheet and need to protect it with a unique serial
number that is provided separately to each customer upon purchase
(i.e., each customer gets a unique number).
How can a procedure be implemented in VBA to validate serial numbers
and to block randomly generated numbers by non-subscribers?
For customer convenience, the number should be around 6 characters
long.

Ideally, that procedure will validate the serial number without having
to index it against a huge database of valid numbers stored somewhere
in the sheet.
Web connectivity, to tap into a central server for number validation,
cannot be assumed.
In a nutshell, what is needed is something akin to serial numbers used
to protect commercial software.

Any help is appreciated.
alseikhan


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