work sheet protection

[Guest]

We program worksheets i.r.o. income tax and financial calculators.
We enter formula into cells, then hide the row, and protect the worksheet /
work book to protect the intelectual property of our formulae.
To our horror we find that the standard protection is easily breached, and
our hidden formulae are then revealed, please, any suggestions?
Also we 'time expire' our programs, but again this is easily circumvented by
'rewinding' the clock, please, any suggestions?
Keepwell
Regards
roger

 

[Dave Peterson]

Don't use excel as your application.

Write your own compiled COM Addin that contains code so you can remove the
formulas from the worksheet cells.

This book may help:

Professional Excel Development
Stephen Bullen, Rob Bovey, John Green

(I've never done it!)