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 today.

Microsoft yesterday said it would be offering a patch to a critical flaw in its Windows operating system next week. Today, however, representatives said that the company had changed its mind and would not be releasing any security patches this month.

Microsoft releases most software patches on the second Tuesday of each month, a date that has come to be known as Patch Tuesday.

The software vendor declined to say exactly what had caused the last-minute change in plans.

"It was a quality issue," said a spokeswoman. "They found something that made them realise that it was best not to release [the patch] this month," she said, adding that the company's security team decided it needed to put the Windows patch through additional testing.

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