Microsoft has explained why it decided not to issue the latest instalment of monthly security updates, maintaining that it needed more time to test the patches.

"The update release process involves a significant testing focus if customers are to get high quality updates," explained Tracey Pretorius, Microsoft's PR manager. "It was a quality issue. We wanted to do some additional testing."

But Microsoft's explanation has not convinced some IT security professionals. "Why would they launch a service that they're not going to be able to keep up?" asked Amar Rathor, managing director of CounterSnipe, a Linux-oriented security service provider.

"Does this sound right? Is Microsoft the sort of company that never releases a product until it's 100 per cent right? There must be something they're not telling us."

But Microsoft insisted that the move was down to quality concerns. " Microsoft will not release an update until it meets those standards," said Pretorius.

The company has, however, been able to release technology updates to combat malware. This month's update removes Bobax, Esbot, Gael, Yaha and Zotob. The Malicious Software Removal Tool is available here. 

Microsoft also released the Update Rollup 1 for Windows 2000 SP4, which addresses a number of installation issues experienced by customers.