Microsoft has issued 10 security updates, fixing critical vulnerabilities in its Windows and Office software. But distribution glitches prevented the software giant from pushing them out to users automatically.

Six of the 10 updates are rated critical, the most serious rating given by Microsoft.

Five of the updates are for Windows, including a patch for 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, considered to be less severe than the worst of the Windows and Office bugs.

The patches were released Tuesday as part of Microsoft's regular monthly security update cycle that can be downloaded from the company’s website (http://www.microsoft.com/technet/security/bulletin/ms06-oct.mspx).

The updates fix a total of 26 bugs in Microsoft's software, making them the largest assortment of Microsoft patches in recent memory.

For many PC users, however, the updates were unavailable for a good part of the day. Microsoft released the software at 11 a.m. 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 about the next five hours.

Microsoft wasn't saying exactly what caused the problem, but Security Response Centre program 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.

Users of Automatic Updates and of Windows Update, version 6, were also affected by the delay, Microsoft said.

The most publicised of these flaws 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.

Microsoft Office has also been the target of a number of extremely limited attacks over the past few months, and on Tuesday Microsoft issued four updates that addressed critical flaws in PowerPoint, Excel and Word, and the Office suite itself. All of these flaws could be exploited by an attacker to run unauthorised software on a victim's computer, Microsoft said.

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 testing. The company has not yet decided whether this Windows operating system update will be released in November, Budd said.

There was one other noticeable omission from this month's cycle of patches.

Hackers have released attack code for a vulnerability in the Microsoft DirectAnimation Path ActiveX control that could be exploited to run unauthorized code on a victim's computer. Microsoft issued a warning about the bug in mid-September (http://www.microsoft.com/technet/security/advisory/925444.mspx) 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."

Yesterday also marked the end of the line for Windows XP Service Pack 1, which will no longer be supported by Microsoft.