A. Microsoft releases security updates when needed on the second Tuesday of each month. Each update is accompanied by a bulletin describing the security updates. This bulletin lets you plan the deployment of the updates and is preceded by an Advance Notification on the Microsoft Web site, which should be posted three business days before the release date at 10:00 A.M. Pacific. You can find the Advance Notification at http://www.microsoft.com/technet/security/bulletin/advance.mspx. You can also subscribe to the security bulletins at http://www.microsoft.com/technet/security/bulletin/notify.mspx.
The main Microsoft Security Bulletin site is found at http://www.microsoft.com/athome/security/update/bulletins/default.mspx.