I very much agree with Joel - Excel is not very password protected and
depending on how advanced they are, it can be broken.

Other than the basic Password protection on a sheet/workbook, you can use an
addin and protect that also then at least they have to have another level of
expertese to get into the file. This may require you sending something to
have them load the macro each time.

"Jeremy" wrote:

I have prepared a pretty advanced spreadsheet to give to a potential
customer. Because this customer does not have an exclusive agreement with my
company, I would like to build in some security so they cannot see the
calculations and base values.

I tried to hide the sheet with the calculations and protect it. On of our
sales guys was able to break this open in less than 20 minutes.

How can I better secure this?