Microsoft has broken its own Patch Tuesday record by patching a record 31 vulnerabilities; its previous record of 26 was achieved in October 2006.

The company issued 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."

"This is a very broad bunch," said Wolfgang Kandek, chief technology officer at security company Qualys, "compared to last month, which was really all about PowerPoint. You've got to work everywhere, servers and workstations, and even Macs if you have them. It's not getting any better, the number of vulnerabilities [Microsoft discloses] continues to grow."

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 the prize at the "Pwn2Own" 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 Pwn2Own sponsor.

Although users running IE8 on Vista or even Windows 7 are somewhat protected from the exploit used to cash in at Pwn2Own, Windows XP users have been at risk for months, Forslof added.

The IE update also caught the eye of Kandek's colleague, Amol Sarwate, the manager of Qualys' vulnerability research lab. "What's interesting is that IE8 only has a single vulnerability," said Sarwate, talking about the Pwn2Own bug. "But IE7 has seven. That's one good reason to go to IE8."

Eric Schultze, chief technical officer at Shavlik Technologies, added two other updates to Storms' IE patch as his fix-first recommendation. "I'd equally patch the IIS, IE and Active Directory vulnerabilities," he said.

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 organisation's] passwords," Schultze said.