A bug discovered is Microsoft Outlook can lead an attacker to take control of a home or business computer. Imagine a hacker gaining control of a CEO’s confidential emails or a hospital, accounting firm, etc. confidential emails. A virus using this flaw could be passed by the infected computer to everyone on the victims email list.
Microsoft issued an update to address this problem which affects Microsoft Office 2007, 2010, 2013, 2016 including Mac versions of Microsoft Office as well. For this full list of affected Office versions: https://technet.microsoft.com/en-us/library/security/ms15-131.aspx
This is why we recommend to turn on Windows updates. Note that some viruses have the capability to disable Windows updates.
For more information about this bug: http://www.securityweek.com/badwinmail-outlook-flaw-puts-enterprises-risk