Excel is blocking untrusted XLL add-ins by default
We are introducing a default change for Excel Windows desktop apps that run XLL add-ins: XLL add-ins from untrusted locations will now be blocked by default.
For XLL add-ins in files from untrusted locations, you will no longer be able to enable content with a click of a button. A message will appear notifying you of the risk and a link to get more information about possible workarounds and support. This change will help you stay more secure by blocking popular attack techniques.