You can make Excel always open old spreadsheets in Protected View. Enable or disable Protected View using in-built setting, Group Policy, Registry.

If you see The file couldn't open in protected view error while opening Microsoft Excel, the fixes listed in this post will help you.

How to Tell If a Worksheet Is Protected in Microsoft Excel 2003. Protecting a worksheet in Excel 2003 prevents others users from editing it. For example, if you have tracked and charted your ...