The advance warning came less than a week after Microsoft acknowledged that exploit code had gone public and was being used by hackers to hijack Windows PCs running IE.
Microsoft will deliver the out-of-cycle patch Wednesday at 1 p.m. Eastern time via its normal update mechanisms, including Windows Update, Microsoft Update and Windows Server Update Services (WSUS).
The update will be pegged "critical," the most serious ranking in Microsoft's four-step scoring system. Microsoft will provide patches to users of Windows 2000, XP, Vista, Server 2003 and Server 2008 for IE5.01, IE6 and IE7. A separate patch will apparently be issued tomorrow for IE8 Beta 2, a preview version of Microsoft's next browser that is not officially on the support list.