You may want to take a look at this, if you use Microsoft Office 2007, 2010, of 2013 — not sure about you 365 people, but you may be included.
Security Advisory by Microsoft
“…The vulnerability could be exploited through Microsoft Outlook only when using Microsoft Word as the email viewer. Note that by default, Microsoft Word is the email reader in Microsoft Outlook 2007, Microsoft Outlook 2010, and Microsoft Outlook 2013.”
It allows an exploit to execute remote code on your machine — not a pretty thing. Follow this article to turn off the setting in Outlook that allows you to preview RTF (you can disable other file-types in the same fashion, such as PDF here, too).
The Security Advisory by Microsoft that I linked above also has Suggested Actions, such as a simple Fix It option that does the configuration work for you. Eventually they’ll come out with a fix, but it looks like the zero-day must have hit someone hard enough for Microsoft to recognize it and warn the community.