Microsoft has decided not to go ahead with its monthly security update after encountering an unspecified quality issue with the software patch it had planned to release tomorrow.

Last week, Microsoft said it would be putting out a critical patch to a flaw in Windows. The next day, however, company representatives said that the company had changed its mind and would not be releasing any security patches this month after all.

Microsoft releases most software patches on the second Tuesday of each month, a date that has come to be known as "Patch Tuesday" by security professionals. The software giant declined to say exactly what had caused the last-minute change in plans.

"It was a quality issue," said a Microsoft spokeswoman. "They found something that made them realise that it was best not to release (the patch) this month."

This is the second time that Microsoft has changed its mind about releasing a patch since the company began giving customers advanced notification of its monthly patches late last year.

It is also the second month in a row that quality issues have marred the monthly software release. In August, Microsoft released a corrupted version of a patch for Internet Explorer, and users who picked up the patch from Microsoft's Download Center within the first few hours of its release were unable to install the software patch.

This month's delay is not related to the corruption problem that occurred last month, the spokeswoman said.

Though it won't be releasing security updates next Tuesday, there will still be some new software for Windows users. Microsoft still plans to update its Malicious Software Removal Tool, and the company will also release an unspecified high priority, "non-security" update, the spokeswoman said.