Microsoft has hit back at VMware after thevirtualisation company accused the software giant of restricting competition.

Responding to comments published in a VMware White Paper, Mike Neil, general manager of virtualisation strategy at Microsoft said that, "claims made in VMware's White Paper contain several inaccuracies and misunderstandings of our current licence and use policies, our support policy and our commitment to technology collaboration."

Earlier this year, Microsoft restated its policy that only Vista Business, Enterprise and Ultimate versions could be used in a virtualised environment. Neil defended that decision in a posting on his blog on 25 February, saying that virtualisation was new for consumers and not yet mature enough from a security perspective for broad adoption. He did say, however, that Vista Enterprise lets users have four instances of Windows installed in VMs.

Since then, Neil has issued a statement saying that, "we believe that we are being progressive and fair with our existing licensing and use policies and creating a level playing field for partners and customers," adding that Microsoft was committed to "high-quality" tech support and working toward interoperable virtualisation technology.

He then turned the tables on VMware, saying "we believe it's better to resolve VMware's claims between our two companies so that we can better serve customers and the industry. EMC is a long-time partner of Microsoft. We've extended this courtesy to VMware due to our mutual customers and partnership with EMC. We are committed to continuing to collaborate with VMware as we have been doing on regular basis. Consistent with this, Microsoft believes that we will be able to accommodate a mutually agreeable solution between our two companies and clear up any existing misunderstanding with regard to the points raised in the whitepaper."

In the whitepaper, VMWare lists a number of objections it has with the way Microsoft is approaching the virtualization market and what it is doing with licensing restrictions and other virtualization capabilities on the current Windows platform and upcoming improvement in Longhorn Server, including high-performance virtual machine technology called hypervisor.