Microsoft has released nine security patches, including three critical fixes for Windows and Internet Explorer.

Among them is a patch for bugs in two separate Windows components that security researchers believe could be exploited in by attackers in much the same way that the Zotob family of worms were used two months ago.

The patches were released late yesterday in the usual monthly security release from the software giant. Two of the critical updates concern Internet Explorer and Microsoft's DirectShow media streaming software. A third, described in Microsoft Security Bulletin MS05-051, concerns the COM+ services included with Windows as well as the Microsoft Distributed Transaction Coordinator (MSDTC), a component of the operating system that is commonly used by database software to help manage transactions.

It is these last two vulnerabilities that have security researchers concerned because of their similarity to the Windows Plug and Play (PnP) system vulnerability reported last August. Within a week of its disclosure, that flaw was exploited by the authors of the Zotob worm. Variations of this attack eventually knocked hundreds of thousands of machines offline, primarily affecting Windows 2000 users.

Microsoft has rated the MSDTC vulnerability as critical for users of Windows 2000, meaning the vulnerability could be used by attackers to seize control of any unpatched system. The COM+ bug is rated critical for Windows 2000 and Windows XP, Service Pack 1.

Security researchers say that another Zotob-style worm outbreak is now a possibility. "The COM+ and MSDTC vulnerabilities have a very similar appearance to the PnP vulnerability that caused Zotob," said Mike Murray, director of vulnerability and exposure research for nCircle.

Internet Security Systems' Neel Mehta, agreed that there were similarities between the PnP bug exploited by Zotob and MS05-051. "The scope of the affected platform is exactly the same and these services are run by default on Windows 2000," said Mehta. "In terms of ease of exploitation, they're not incredibly difficult to exploit, but they're not as easy as the Plug and Play vulnerability."

Mehta is also concerned with the DirectShow bug. By tricking users into viewing malicious programs that appeared to be legitimate multimedia files, attackers could seize control of unpatched Windows systems, he said. "It requires user interaction of some sort, which takes it down a notch from MS05-051, but it is still a serious vulnerability."

Microsoft has rated the DirectShow flaw "critical" for a wider range of Windows systems than the COM+ and MSDTC bugs. It has been rated critical for Windows XP, Windows 2000, Windows Server 2003, Windows 98 and Windows ME.

Though the COM+ and MSDTC bugs will probably get a lot of attention, because they could be used in worm attacks, the DirectShow or IE flaws are also dangerous, and could be used by thieves as the basis of a targeted attack, said Marc Maiffret, chief hacking officer with eEye Digital Security Inc. "The other vulnerabilities I think of as worse in a way because it's an easier way to target a specific corporate user," he said.

The other security updates released Tuesday include "important" patches for Client Services for NetWare, the Windows Plug and Play system, Microsoft Collaboration Data Objects, and the Windows Shell. "Moderate" bugs have also been patched in the Windows FTP client and the Network Connection manager.

Tuesday's flurry of releases comes after a very quiet September for Microsoft's security team. Last month, Microsoft had planned to release only one security patch, but ended up scrapping the update at the last minute due to "quality issues".