Microsoft on Tuesday released 10 security updates, one less than anticipated, that patched a record 26 vulnerabilities in Windows, Office, and .Net. More than half of the flaws were pegged "critical" by the Redmond, Wash. developer.

Tuesday's tally was impressive by any count: 6 of the 10 updates were judged critical, with the remaining split among Microsoft's other rankings: "important" (1), "moderate" (2), and "low" (3). Of the 26 disclosed vulnerabilities, 15 were labeled critical, 6 important, 2 moderate, and 3 low. Both the total vulnerabilities and the number of critical vulnerabilities set new records for Microsoft in its monthly patch process.

"This is very rich lot," said Minoo Hamilton, a senior security researcher with patch management vendor nCircle. "There's everything in here from Windows Explorer and Internet Explorer to Word and Excel and PowerPoint."

Every one of the half-dozen bulletins marked critical should be paid attention, said Hamilton. "They're all remotely exploitable, and in some cases across the [OS] board."

Several of the updates fix flaws that hackers are already exploiting, including MS06-057, which patches the WebViewFolderIcon bug known -- and used -- since the end of September. Others patching already-exploited vulnerabilities include the MS06-058 update for Microsoft Office PowerPoint and MS06-060, a fix for Microsoft Word.

Office, in fact, accounted for 62 percent of the bugs patched Tuesday and 86 percent of those marked critical. Microsoft's suite has been under the gun since May, when a vulnerability in Word was fixed, and has been the subject of prognosticators for months.

"Attackers have an increasing tendency to exploit vulnerabilities in desktop applications rather than network infrastructure," said Oliver Friedrichs, director of the Symantec's security response team, in an e-mail. "The quantity of Microsoft Office vulnerabilities this month illustrates this emerging attacker focus and users should consider the installation of these patches to be critical."

The Office vulnerabilities make lucrative targets for attackers, added Don Leatham, the director of solutions and strategy at Patchlink. "The hacker community is driving more and more toward creating as many botnets as possible, and the easiest way to get them is in the end-user part of the enterprise. The number of bugs within Office shows that concerted effort." All the Office updates affect not only various versions on Windows, but also Mac Office 2004 and Mac Office v. X. Mac users can update from within the suite, or by downloading the appropriate patch at Microsoft's Mactopia Web site.

But the update that both Leatham and nCircle's Hamilton thought deserved first place in the patching order wasn't one of the 4 for Office, but instead MS06-061, a fix for the XML parser and XML core services within Windows. This critical update, said both researchers, should be patched pronto.

"The XSLT buffer overrun is critical across the board, Windows 2000, XP, and Server 2003," said Hamilton. "This one will be great for phishing and Web hacking because of the prevalence of XML and the ease of exploit."

Leatham agreed, and then some. "This one is really, really concerning us. I'd expect this to be a prime vulnerability that will definitely be targeted for exploit. Click on the wrong link and you're infected."

The problem, according to Microsoft's notes on the vulnerability, is compounded by a lack of workarounds or factors that might minimize the threat. Microsoft had no workarounds to offer up other than to patch, and the only way to guarantee safety is to surf only trusted sites.

"All an attacker has to do is build a page, get people there, and if XML is running, the buffer's overrun and remote code can be downloaded," said Leatham.

Other bulletins issued Tuesday quash bugs in the Server service; the next-generation TCP/IP protocol, IPv6; and .Net Framework 2.0. None of those updates were marked higher than important, Microsoft's second-from-the-top threat ranking.

One update, however, went missing Tuesday. Last week, in its regular Thursday-before-patch-day announcement, Microsoft said it would issue 11 bulletins, 6 of which would affect Windows. Tuesday saw 10 bulletins, with only 5 for Windows.

"We found an issue in our testing after the Thursday notification in one of the Windows Updates that caused us to remove that update from the release channel while we put it through additional testing," a Microsoft spokesperson said. "[We] will make it available in the next release cycle once it reaches the quality bar."

Microsoft has reason to hesitate, said Hamilton, who noted the firm has had to re-release updates recently. The quality of its August batch was especially suspect; Microsoft had to reissue three different bulletins from that month, including one that was revised twice.

Users can obtain Tuesday's patches via Windows' Automatic Update, from the Microsoft Update service, or through other Microsoft software and services, including the enterprise-grade Windows Server Update Services (WSUS) and Software Update Services (SUS).