Attackers are actively exploiting a newly discovered Microsoft Word vulnerability that could be used to gain remote access of your PC, according to Microsoft, and even worse, the exploit can be triggered by opening or merely previewing a malicious email using Outlook's default settings.
The attack is delivered using booby-trapped Rich Text (RTF) files. Accessing or previewing a poisoned file with Word grants the attacker the same rights as the current user.
Making matters worse, Word is the default document viewer in Outlook 2007, 2010, and 2013.
Currently, Microsoft is only aware of the limited, targeted attacks against Word 2010, but the same vulnerability affects Word 2013, Word 2013 RT, Word 2007, Word 2003, Microsoft Office for Mac 2011, and related programs like Word Compatibility Viewer and Word Automation Services on Microsoft SharePoint Server.
Microsoft's released a Fix It that neutralizes the exploit by going the nuclear route and barring all RTFs whatsoever. That may not be an option for you, seeing as how the RTF format is a popular alternatives to Microsoft's .DOC format and widely used by non-Office productivity programs. If so, there are a couple of workarounds you can use to mitigate the risk until Microsoft patches it up:
Configure Outlook to read emails in plain text.
Try to stay away from RTF files, but if you have to open one, scan it with security software first. This should be standard security practice for all downloads.
Use a limited account in Windows, rather than an Administrator account, for your day-to-day PC usage. That way the attacker receives far more limited access to your machine if you do become infected. In fact, this one simple trick can make your PC virtually invulnerable.
Microsoft says running its Enhanced Mitigation Experience Toolkit (EMET) can also protect against the exploit, as is often the case with zero-day attacks.
Finally, note that the exploit also involves Word 2003, and Office 2003 is going end-of-life on April 8, just like Windows XP. That means no more security patches for situations just like this, and Office is a common attack vector for baddies. Yes, it's going to be hard to ditch Office 2003's traditional file menus, but staying safe in the future means upgrading and learning to love the Ribbon, folks.