Is there any way (in Excel 2003) in which a formula in a locked cell of a
password protected worksheet can end up corrupted, without the sheet having
first been unprotected?

I recently created a workbook with password protected worksheets, which
accepts data entry in some unlocked cells and carries out data analysis by
formulas in locked cells. There are no macros in the workbook.

I was asked to investigate when the analysis stopped functioning correctly,
and I found some of the formulas in the locked cells had become corrupted,
but I have no idea how this could have happened - without somebody hacking
the worksheet password. Before I investigate a possible hack I just need to
know if there are any other ways the formula corruption could have occurred
without a password hack.

Any help gladly appreciated.