Important - Microsoft Security Advisory - for all MS-OFFICE users

Scenario
In an email attack scenario, an attacker could leverage the DDE protocol by sending a specially crafted file to the user and then convincing the user to open the file.

Mitigating DDE Attack Scenarios
Users who wish to take immediate action can protect themselves by manually creating and setting registry entries for Microsoft Office. Use the following instructions to set the registry keys based on the Office applications installed on your system.


For More:
https://technet.microsoft.com/library/security/4053440