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

Critical is Microsoft’s highest vulnerability rating.

A summary describing briefly the vulnerabilities is available from Microsoft’s Security Bulletin Summary for October 2007.
From this page you will also find links to more detailed information in Microsoft's Security Bulletins MS07-055 - MS07-060.

The four critical updates address the following issues:

• One privately reported vulnerability in Kodak image viewer.
• One privately reported vulnerability in Outlook Express and Windows Mail.
• Vulnerabilities in Internet Explorer, three privately reported and one that is disclosed in public.
• One privately reported vulnerability in Microsoft Word.

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.