It is reported that spreadsheet passwords can be foiled by simply copying and pasting cells. When the spreadsheet data is copied using the "copy all" command and then pasted into a new spreadsheet, the hidden and password-protected cells reportedly can be exposed. A local user can execute the "unhide" command to view the data. Also, in other non-Microsoft spreadsheets, the hidden cells may be revealed automatically.

There was no solution from Microsoft at this time.
http://www.nwfusion.com/news/2001/1217excel.html