If you woke up this morning and noticed that your PC had rebooted overnight, don't be alarmed--or at least any more alarmed than usual. A Windows reboot was part of the plan, as Microsoft issued patches for 10 security fixes yesterday, three of which are critical. The fixes shipped to customers via Automatic Updates and Windows Update as part of Microsoft's monthly security fix release.
  
The critical patches issued yesterday are for Microsoft Internet Explorer (IE) and all supported versions of Windows. Microsoft also issued "important" patches for Microsoft Outlook Express, Outlook Web Access (OWA) for Microsoft Exchange Server 5.5, Web Client Service, and Windows Step-by-Step Interactive Training. Patches for ISA Server 2000, Microsoft Agent, and Telnet Client were rated "moderate."
  
Additionally, Microsoft reissued three previous patches to fix problems with the original fixes. For more information about Microsoft's security patches, visit the Microsoft Security Web site.

http://www.microsoft.com/security