Microsoft has released patches for a record 26 holes in no less than 10 security updates, six of them critical.

It is the largest number ever dealt with on "Patch Tuesday" - the software giant's security update cycle which takes place on the second Tuesday of the month. Five of the updates cover Windows, including a nasty bug in the operating system's graphical user interface, which is currently being targeted by attackers. Four updates are for Office, and the final update is for the .Net framework.

To make matter worse, the updates were unavailable for most of the (US-time) day. Microsoft released the software at 11am Pacific time, but a networking problem prevented users of Microsoft Update and Windows Server Update Services (WSUS) from being able to download the software for the next five hours.

Microsoft won't saying exactly what caused the problem, but Security Response Center manager Christopher Budd blamed a "networking issue" that kept the patch from being properly copied between Microsoft's internal staging systems and those used by its customers. It was the first time Microsoft's updates had been delayed by this particular problem, Budd said.

The most publicised flaw is a bug in an ActiveX control called WebViewFolderIcon, which is used by the Windows' graphical user interface software. This vulnerability was first disclosed in July, but hackers began exploiting it late last month after exploit code taking advantage of it was added to the Metasploit hacking tool.

Four updates addressed critical flaws in PowerPoint, Excel and Word, and the Office suite itself. All could be exploited by an attacker to run unauthorised software on a victim's computer, Microsoft warned. The sixth critical update fixes two vulnerabilities in the XML (Extensible Markup Language) parser used by Windows.

Microsoft had planned to issue an 11th update on Tuesday but pulled it at the last minute to give it more time for testing. The company has not yet decided whether this Windows operating system update will be released in November, Budd said.

However there was one other noticeable omission from the cycle: a hole in the Microsoft DirectAnimation Path ActiveX which hackers have already released attack code and could be exploited to run unauthorized code on a victim's computer. Microsoft issued a warning about the bug in mid-September but has not yet finished development of a patch for the problem.

"We're still in the investigation process," Budd said. "We've just not completed the development of an update ... that reaches our standard quality bar for our release."

Original reporting by Robert McMillan, IDG News Service