All versions of IE (IE6-IE11) are vulnerable to a remote code execution which works through a memory corruption bug. Attacks have been reported, so this isn’t a ‘theoretical’ thing. The reported attacks are using attacks on IE8 and IE9. The source for this is http://technet.microsoft.com/en-us/security/advisory/2887505 :

“Mitigating Factors:

• By default, Internet Explorer on Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability.
• By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML email messages in the Restricted sites zone. The Restricted sites zone, which disables script and ActiveX controls, helps reduce the risk of an attacker being able to use this vulnerability to execute malicious code. If a user clicks a link in an email message, the user could still be vulnerable to exploitation of this vulnerability through the web-based attack scenario.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
• In a web-based attack scenario, an attacker could host a website that contains a webpage that is used 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. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker's website.”

So, if you’re running IE on Windows Server 2003, 2008 R2, 2012 and 2012 R2 the vulnerability is mitigated.

There are work arounds and they are on the security advisory link above under “Suggested Actions”.

Another ‘work around’ is using FF or Chrome until a real fix comes along. MS is still debating about a patch for it.