In their advance notification, the Redmond company announces to release 2 Security Bulletins on the May 2010 Patchday next Tuesday. They fix vulnerabilities within nearly all currently supported Windows operating systems and in Microsoft Office, also in Visual Basic for Applications. Both vulnerabilities get marked as critical by Microsoft.
The Windows Patches require a restart, and the Office / Visual Basic for Applications Updates may require a restart. Administrators and users should get prepared to install the Updates on Tuesday ASAP, as the vulnerabilities they fix can lead to system infection without much user interaction. As usual, no further details are published by Microsoft in the advance notification.