Vista will not make it more difficult for anti-virus systems to work, Russian computer security group and potential IPO candidate Kaspersky Lab said on Friday, contradicting rivals. In an open letter this week, U.S. anti-virus provider McAfee accused Microsoft of weakening users' protection by no longer co-operating with computer security groups and denying them access to the core of the Vista system.

"From what we have seen of Vista we cannot tell that Microsoft is blocking access to the core," Kaspersky Lab Chief Executive and co-founder Natalya Kaspersky told Reuters in an interview in Paris.

"It would not make any sense for them (Microsoft) to stop working with other computer security companies because it would make their system more vulnerable to attacks," Kaspersky added.

Microsoft, the world's largest software group, entered the computer security market in June by introducing OneCare, a software product aimed at protecting computers from viruses, spyware and other ailments.

The U.S. software giant fired back on Monday, saying that it had worked closely with computer security companies throughout the development of Vista and planned to continue to do so.

"Microsoft would have to change their business completely if what McAfee says was true," Kaspersky said, explaining that Microsoft's business model was based on working with other providers.