Today Microsoft posted their security bulletin for December. As usual all required security updates for your PC can be found on Windows Update.
Bulletin MS05-054: Cumulative Security Update for Internet Explorer (905915) [Critical] Vulnerabilities exist in Internet Explorer, the most severe of these could allow an attacker to take complete control of an affected system.
Bulletin MS05-055: Vulnerability in Windows Kernel Could Allow Elevation of Privilege (908523) [Important]A vulnerability exists in the Windows Kernel that could allow elevation of privileges on an affected system. An attacker must have valid logon credentials and be able to log on locally to exploit this vulnerability.