Critical Windows patch causes 'serious problems'

A Microsoft patch meant to fix critical security flaws in Windows 2000, Windows XP and Windows Server 2003 is causing trouble for some users, the company said on Friday.

The patch was released on Tuesday to fix four Windows flaws, including one experts predict will be exploited by a worm in the coming days. The flaw, tagged "critical" by Microsoft, lies in a Windows component for transaction processing called the Microsoft Distributed Transaction Coordinator, or MSDTC.

Installing the patch can cause serious problems, Microsoft said in an advisory posted to its website on Friday. The patch could lock users out of their PC, prevent the Windows Firewall from starting, block certain applications from running or installing, and empty the network connections folder, among other things, the software maker said.

The trouble appears to occur only when default permission settings on a Windows directory have been changed, according to Microsoft. The software maker has received "limited reports" of problems from customers but is still investigating the issue, a representative said.

Even if users experience PC trouble after installing the patch, they will still be protected against any attack exploiting the Windows flaw, a Microsoft representative said. The patch was delivered with Microsoft security bulletin MS05-051.

To resolve any problems caused by the MS05-051 patch, users should restore the default permissions for the Windows folder and the COM+ catalogue. A guide is available on the Microsoft website, and steps start with changing the permissions on the "registration" folder in the Windows directory.

Joris Evers writes for CNET News.com