In its security bulletin summary for January 2011 Microsoft has published one update for critical and one update for important vulnerabilities in its operating systems / applications.
Critical is Microsoft's highest vulnerability rating.
A summary describing briefly the vulnerabilities is available from Microsoft's Security Bulletin Summary for January 2011.
From this page you will also find links to more detailed information in Microsoft's Security Bulletins MS11-001- MS11-002.
The critical update addresses the following issue:
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.
Note in particular that neither the unpatched vulnerability in Internet Explorer (Norman's Security Advisory 23 December 2010), nor the vulnerability in Windows Graphics Rendering Engine (Norman's Security Advisory 5 January 2011) are among the issues addressed in this monthly update from Microsoft.
See Microsoft Security Response Center for more information about this.
Norman advices all affected users to download the relevant security updates as soon as possible, to be protected from potential exploits.