The brand spanking-new Windows operating system called Vista - billed as "the most secure version of Windows yet" on the Microsoft Web site - has proven a pushover for Internet hackers.

Microsoft has acknowledged Vista has a flaw that could allow users to increase their access level to administrator, a problem first posted by a Russian hacker.

A flaw was also found in Microsoft's new Internet Explorer 7 that could download viruses from a booby-trapped Web page. That flaw and five others were reported by Determina, a Silicon Valley computer security company.

"We are closely monitoring developments," said Microsoft's Mike Reavey, operations manager for the Redmond, Wash. company's emergency response team.

"Currently we have not observed any public exploitation or attack activity regarding this issue," he wrote.

And, he insisted, "I still have every confidence that Windows Vista is our most secure platform to date."

But news of the IE7 flaw and the hacker postings is a black eye for Bill Gates and Microsoft - and for the thousands of PC makers who will begin selling their computers next month with Vista.

Thousands of consumers put off buying computers this Christmas season waiting for the release at the end of January of the new upgrade from Windows XP to Windows Vista.

One online tech expert, Jay Dougherty, wrote for the German Press Agency that Vista may prove a tough sell for folks already happy with their home computers, especially because the current XP system has proven to be relatively stable.

"People are tired of upgrading - especially when the benefits of doing so are difficult to articulate or uninspiring. That's the problem with Microsoft's Vista operating system in a nutshell," he wrote.

Vista's big selling points, besides it supposed safety and security, are its stunning 3D graphics that many critics argue is simply an attempt - and a bad one at that - to match what Apple has had for years on the Macintosh.