Microsoft has released a security advisory for an Internet Explorer zero-day vulnerability, which is an attack or threat that exploits a previously unknown vulnerability in a computer application and has not yet been addressed or patched by the vendor. The vulnerability affects all supported versions of Internet Explorer. It is reported systems are being compromised when the vulnerability is exploited.
Microsoft Internet Explorer 6-11
The IT Security Office recommends using an alternate web browser until a patch is released by Microsoft. For more technical owners, Microsoft suggests the Enhanced Mitigation Experience Toolkit 4.1 (EMET) to help block the attack. 
US Cert: Microsoft Internet Explorer use-after-free vulnerability
Microsoft Security Advisory 2963983
Additional information about this vulnerability can be viewed at:
If you have any questions, please contact the IT Service Center at 303-735-4357 (or 5-HELP from an on-campus phone) or firstname.lastname@example.org.
OIT has defined the following categories to describe the severity of security risks:
URGENT severity represents a broad threat to the entire campus community.
SEVERE severity included remote exploits and worms.
IMPORTANT severity includes virus and local exploits for commonly used services.