In the biggest one-day security update since February, Microsoft Tuesday issued nine bulletins that patched 14 vulnerabilities in Office, Internet Explorer (IE), and every edition of Windows. Eight of the fixes were pegged as critical, the company's highest risk rating.

Faced with an overload of vulnerabilities -- including some in components that Microsoft has patched in the past -- researchers squabbled over which should get priority.

"I think six of these are equally important," said Andrew Storms director of security operations at nCircle Network Security.

"The GDI vulnerability is the most critical," said Amol Sarwate, the manager of Qualys' vulnerability research lab.

"MS07-042 affects everything," said Don Leatham, the director of solutions and strategies at PatchLink.

The only update that all three agreed should be moved to the top of the list was the one that patched a bug in Windows Graphics Rendering Engine (GDI). According to Microsoft's MS07-046 advisory, the GDI bug not only affects Windows 2000, XP and 2003 Server, but a successful attack could give the hacker complete control of the PC.

"This affects a core Windows subsystem, and all versions except for Windows Vista," said Sarwate. "Unlike most other vulnerabilities, this one doesn't need an application, like Internet Explorer; all that's needed is a [malformed] image file. The only good news here is that this does not affect Vista."

PatchLink's Leatham called out the GDI bug as one of two he said should be patched immediately, and rang the alarm even louder than Sarwate. "This has the potential to be as dangerous as the WMF vulnerability [from late 2005]," he said. "Microsoft makes it sound as if the typical exploit would come as some sort of e-mail attachment, but the GDI is used by about every single Microsoft application out there.

"Hackers will look at this like Nirvana, something this low level that they can use to target about every workstation in an enterprise," warned Leatham.

The WMF (Windows Metafile) vulnerability, which raised a ruckus at the end of 2005 when hackers began widely exploiting the zero-day bug, was patched in early 2006 by one of the rare out-of-cycle fixes that Microsoft has issued. Even today, the WMF exploit impact on Windows users remains among the largest ever.

Eight other bulletins, however, will vie for administrators' attention. Some, said Storms, Sarwate and Leatham, should get that attention before the others. Among the fixes they pointed to:

-- Storms: "The idea of virtualization is a really big thing in IT today, and everyone who does it in the enterprise has the same concern: can the guest OS [in a virtual machine] affect the host OS?" For that reason, he put the spotlight on MS07-049, even though the update was rated important. "The number one concern running virtualization software in the enterprise is 'How much can we trust the guest OS?'" he said. The bug patched today could let users with administrative privileges on the guest OS run code on the host operating system, or even on another VM's guest OS, reported Microsoft.

-- Sarwate: "MS07-045 affects all versions of Internet Explorer. This vulnerability is in the Cascade Style Sheets [CSS], which are the building blocks of any site. According to Microsoft's advisory, IE's parsing of certain strings in CSS is flawed; attackers could exploit it by enticing users to a malicious Web page, resulting in a full PC hijack.

-- Leatham: "MS07-042 affects everything." The vulnerability, which exists in multiple versions of XML Core Services, the component that provides interoperability between several scripting languages, including JScript, Visual Studio and XML applications, affects every supported version of Windows, including Vista. Microsoft rated the bug as critical across the board. "There's so much going on with XML in enterprises," said Leatham. "That's why this is so dangerous."

Microsoft also patched flaws in Excel -- yet another vulnerability in a Microsoft Office document format -- Windows Media Player, Windows' Vector Markup Language (VML) and three of the Microsoft-made gadgets bundled with Vista.

"This is a good batch," said nCircle's Storms, but not in a nice way. "There are a lot of 'Criticals' here, and on the trends and patterns side, a lot of what I call 'repeat offenders.'" By that, Storms meant new patches that Microsoft has had to lay atop code or components patched one or more times before. "Excel is a repeat offender, so is GDI. VML is too, and XML Code Services."

As usual, Microsoft's monthly updates have been posted to Microsoft Update and Windows Update services, and can also be retrieved through Windows Server Update Services (WSUS). The necessary files can also be downloaded directly from Microsoft's Web site.