Internet Explorer CSS vulnerability
This vulnerability affects all versions of Internet Explorer where an attacker can execute remote code with the same user rights as the local user. The attacker can use a web page with specially crafted content that could exploit this vulnerability. Users may end up on a similar web page through malicious links in E-mail or Instant Messenger messages.
It is recommended to use a good anti-virus program or an IDS/IPS system as a countermeasure which according to Microsoft have been quite effective at detecting and blocking attacks.
For more information on how to mitigate this risk visit Microsoft Security Advisory 2458511.