Users' computers can be compromised if they open a specially crafted RTF file using an affected version of Microsoft Word, or they preview or open a specially crafted RTF email message in Microsoft Outlook while using Microsoft Word as the email viewer. Microsoft Word is the default email reader in Microsoft Outlook 2007, Microsoft Outlook 2010, and Microsoft Outlook 2013.
The exploitation of the vulnerability can result in the attacker gaining administrative user rights on the machine (i.e. complete control of the system) if the user uses an admin account.
"In a web-based attack scenario, an attacker could host a website that contains a webpage that contains a specially crafted RTF file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability," they explained.
Users can be lured to visit such websites via spam emails and IMs.
Luckily for everybody who's worried about being targeted, Microsoft has made available a Fix it tool that prevents the flaw to be exploited, at least until a permanent fix is issued.
If, for whatever reason, you don't want to use the Fix it, there are several possible workarounds for temporarily solving the issue (See under "Suggested Actions").
No more details about the ongoing attacks have been shared. It is only known that three individuals of the Google Security Team reported the vulnerability.