Microsoft has unveiled a dozen security updates that patched 20 vulnerabilities, including one found in every security product of its consumer and enterprise lines, including software either bundled with or able to run on the new Windows Vista operating system.

More than half of the 20 patches – 11 total – were labelled "critical," the highest rating in Microsoft's four-step threat scoring system.

Among the updates are several that tackle long-standing problems in numerous editions of Microsoft Office, including six patches for Word, and one each for PowerPoint and Excel.

But the update deemed by analysts to be most important is MS07-010, which patched a critical bug in the malware scanning engine used by Windows OneCar and Defender, Forefront Security and Antigen products. The flaw, said Microsoft, could be used by a hacker to hijack a supposedly protected PC because the scanning engine improperly parses portable document format (PDF) files. Attackers could feed malformed PDFs to PCs via email, for instance, and grab control of the machines without any interaction from users.

But according to Microsoft, the scanning engine bug hasn't been used yet by attackers.

No matter, said Amol Sarwate, who manages Qualys' vulnerability lab. "MS07-010 is the most critical of the bulletins. The flaw in the core protection engine of several Microsoft [security] products can be used to execute attack code on a machine without any user interaction. And this [is the software] which is supposed to protect your desktops and servers from attack."

Symantec's alert to customers of its DeepSight threat network, for instance, rated MS07-010 as a "10" out of a possible 10 on its urgency scale. And Minoo Hamilton, senior security researcher with patch management vendor nCircle, said the patch was not only a critical fix, but an embarrassment to Microsoft.

"There have been so many vulnerabilities having to do with parsing files," said Hamilton, "that this is exactly the kind of thing that you would have expected Microsoft to catch. They'll have to put more effort into securing their security software because this is embarrassing."

But Lamar Bailey, the senior X-Force operations officer at IBM's Internet Security Systems (ISS), disagreed. "These products automatically update, so the exposure will be short," said Bailey. "I wouldn't be surprised if they hadn't already updated themselves."

Instead of the malware bug, Bailey tagged MS07-016, the bulletin that patched three flaws in Internet Explorer (IE), as the one ISS feels should be deployed right away because of a vulnerability in how IE processes requests from file transfer protocol (FTP) servers.

"Lots of shareware sites actually use links to an FTP server," said Bailey. "Users don't always know that they're even connecting to an FTP server." Attackers could entice users to malicious web sites hosting innocent-looking files for downloading, while they're actually exploiting the IE bug to hijack the PC.

Of the three IE bugs in MS07-016, two affect the newest version of the browser, IE 7, on Windows XP and Windows Server 2003f, although the threat rating has been downgraded to "Important." IE 7 on Vista is not at risk, said Microsoft.

Another bulletin, MS07-014, has been long anticipated. The update for Microsoft Word 2000, Word 2002, Word 2003 and Word 2004 for Mac patches six bugs, four of which have already been used by hackers. "We recommend that users also patch this immediately, since exploits are in the wild," said Jonathan Bitle, Qualys product manager.

Three of the four already-used vulnerabilities date back to December, and were reportedly scheduled for release last month before being pulled at the last minute for quality issues.

Other bulletins in the massive patch day – Tuesday's tied a record with two months in 2006 when Microsoft also released a dozen updates – fixed flaws in Windows, Office, Visual Studio, various ActiveX controls, the rich text file (RTF) format, Microsoft Excel and Microsoft PowerPoint.

Users can obtain the February patches via Windows' Automatic Update, from the Microsoft Update service, or through enterprise tools such as Windows Server Update Services (WSUS) and Software Update Services (SUS).