By default, the DDE mode remains disabled in Excel. But if it is enabled, you may experience issues with excel, like problems launching Excel or Excel files. Check if this mode is enabled or not.

Microsoft Office 2010 includes a new "Protected View" that, by default, will open all Outlook attachments and documents downloaded from the Internet in "read-only" mode.

Once you have protected all of the cells, you need to protect your Excel worksheet for the protection to take effect. Click on the Review tab in the top menu bar.