It's Patch Tuesday this week;Microsoft Security Bulletin Advance Notification
On Tuesday 3 April 2007 Microsoft is planning to release:
Security Updates
One Microsoft Security Bulletin affecting Microsoft Windows. The highest Maximum Severity rating for these is Critical. These updates will require a restart. These updates will be detectable using the Microsoft Baseline Security Analyzer.
Microsoft Windows Malicious Software Removal Tool
Microsoft will not release an updated version of the Microsoft Windows Malicious Software Removal Tool on Windows Update, Microsoft Update, Windows Server Update Services and the Download Center on Tuesday 3 April 2007.
Non-security High Priority updates on MU, WU, WSUS and SUS
Microsoft will not release any NON-SECURITY High-Priority Updates for Windows on Windows Update (WU) and Software Update Services (SUS) on Tuesday 3 April 2007.
Microsoft will not release any NON-SECURITY High-Priority Updates on Microsoft Update (MU) and Windows Server Update Services (WSUS) on Tuesday 3 April 2007.
http://www.microsoft.com/technet/security/bulletin/advance.mspx
Please see also: http://blogs.technet.com/msrc/archive/2007/04/01/latest-on-security-update-for-microsoft-security-advisory-935423.aspx on why MS will release security update this week.