In its security bulletin summary for December 2007 Microsoft has published three updates for new critical vulnerabilities in its operating systems / applications as well as four important.

Critical is Microsoft’s highest vulnerability rating.

A summary describing briefly the vulnerabilities is available from Microsoft’s Security Bulletin Summary for December 2007.
From this page you will also find links to more detailed information in Microsoft's Security Bulletins MS07-063 - MS07-069.

The three critical updates address the following issues:

• Two privately reported vulnerabilities in Microsoft DirectX.
• One privately reported vulnerability in Microsoft Media.
• Four privately reported vulnerabilities Internet Explorer.

Updates that fixes the vulnerabilities are available from Windows automatic update mechanism for systems that support this. Alternatively, one may download updates from http://windowsupdate.microsoft.com.  

Norman advices all affected users to download the security updates as soon as possible, to be protected from potential exploits.