Excel – How to prevent the privacy warning in Excel

1) Exit Excel 2007.
2) Start Registry Editor.
3) Locate and then click the following registry subkey:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security

4) On the Edit menu, point to New, and then click DWORD Value.
5) Type ExtensionHardening, and then press ENTER.
6) Right-click ExtensionHardening, and then click Modify.
7) In the Value data box, type 0, and then click OK.

The following list contains the value data settings that are appropriate for the ExtensionHardening setting:

0: Do not check the file name extension and the file type, and bypass the function of the warning message.
1: Check the file name extension and the file type. If they do not match, display the warning message.
2: Check the file name extension and the file type. If they do not match, do not open the file.

Note: The default value data is 1. When the value data is set to 1, the behavior becomes the same as when no registry value is set. When the value data is set to 0, the file name extension and the file content are not checked in all situations. It is not recommended bypassing this function.

8) On the File menu, click Exit to exit Registry Editor.

It seems that the .xls file (Microsoft Excel 97-2003 format) is actually an .xlsx file (Microsoft Excel 2007 format). Changing the file extension from .xls to .xlsx should clear the warning message.