Another Microsoft security vulnerability

Microsoft are about to release an emergency security update to plug a vulnerability which could allow an internet worm to be spread via a computer without the user doing anything. This update is rated as critical for users of Windows 2000, XP and Server 2003 and the less severe rating of "important" for users of Windows Server 2008 and Windows Vista. The patch is scheduled for release at 10.00am Pacific Time (6pm BST) with a webcast 3 hours later to explain the issues. Here is Microsoft's current explanation; useful?