On December 29 2012 Microsoft announced a use after free vulnerability in Internet Explorer. This vulnerability could allow a remote attack to execute code on a user's machine if the user visits a specially crafted website using Internet Explorer.
Reason for detection
Websense Advanced Classification Engine contains real time analytics which identifies code that is trying to use this vulnerability to exploit the user's computer.
Websense has more information available about this threat in this Websense Security Labs post.
For more information about this vulnerability, see Microsoft Advisory 2794220.