Microsoft has issued 10 security updates that patches a record 31 vulnerabilities in Windows, Internet Explorer (IE), Excel, Word, Windows Search and other programs, including 18 bugs marked "critical."

Of the 10 bulletins, six patched some part of Windows, while three patched an Office application or component, and one fixed a flaw in IE. Eighteen of the' 31 bugs were ranked critical, Microsoft's most serious ranking in its four-step score, while 11 were tagged as "important," the next-lowest label, and two were judged "moderate."

The total bug count was the most patched by Microsoft in a single month since the company began regularly-scheduled updates in 2003. The previous record of 26 vulnerabilities patched occurred in both August 2008: and August 2006.
Security experts were all over the map when it came to naming which fixes to deploy first.

"IE's, by far, takes the cake," said Andrew Storms, director of security operations at nCircle Network Security. "It's a client-side bug, there are eight CVEs and there's no doubt that it will be exploited."

As Storms said, MS09-019 patches eight separate vulnerabilities in Microsoft's Internet Explorer browser. One of the patches finally plugs the hole that a researcher used in March 2009 to hack IE and walk off with "Pwn20wn" challenge.

"If you're running IE8 on Windows XP, or are concerned about intranet-based attacks, I would highly recommend putting this update on your high priority 'to do' list," said Terri Forslof, the manager of security response at 3Com's TippingPoint, the Pwn20wn sponsor, in an e-mail today.

Although users running IE8 on Vista or even Windows 7 are somewhat protected by that operating system from the exploit used to cash in at Pwn20wn, Windows XP users have been at risk for months, Forslof added.

The Internet Information Server (IIS) flaw affects some systems that have enabled WebDAV (Web-based Distributed Authoring and Versioning), a set of extensions to HTTP used to share documents over the Web. Schultze put the spotlight on MS09-020 because Microsoft had publicly acknowledged the bug last month in a security advisory.

MS09-018 got his attention because Microsoft pegged the Active Directory flaw as critical, and it could be exploited remotely by simply sending a server a malicious data packet. "Someone could use this to take over Active Directory, and if they do, they'd own all [an organization's] passwords," Schultze said. Three of the security updates, MS09-021, MS09-024 and MS09-027, addressed one or more issues each in Microsoft's popular Office suite.

None of the researchers contacted today put the Office patches near the top of their to-do list. Storms explained why: "Office in general is usually not without bulletins," he said. "This month it's Excel, Works Converter and Word. »