Dropped password
 

I locked cells in an excel spreadsheet and used a password to protect the
sheet.
However, when the users copy the file to their computer, add data, and
return the file or if the user has a different version of Excel (97 vs
97-2003 compatible), the file loses the password requirement. Once the user
copies the file, they can select "unprotect" the sheet without entering the
password.

Is there a way to maintain the password if the file is copied to another
computer or version of Excel?