VMware has come out fighting against Oracle's release of its Oracle VM virtualisation suite.

VMware described Oracle VM as "unproven" and lacking many of the features of its own software.

The firm also pointed out that it already runs more Oracle applications on its virtualisation software than any other virtualisation supplier.

"Oracle's introduction of yet another variant of Xen is clearly a response to the significant virtualisation industry that VMware has established," said Parag Patel, vice president of alliances at VMware.

"The offering does not address the capabilities required to achieve the cost savings and IT simplification that customers are realising everyday from VMware's Virtual Infrastructure.

"It is also an unproven offering and lacks features that VMware customers value and view as key to a virtualisation deployment, including high availability, integration with third-party back-up software and extensive hardware certifications."

Patel added that his company had certified almost 2,000 different hardware models and 30 guest operating systems in the past six years, claiming that nearly half of VMware's customers had a "VMware first" policy.

A full scale war between the two companies looks unlikely, however, as VMware has pledged to work closely with Oracle to ensure future software compatibility.

Oracle's announcement sparked a sell-off of VMware shares by nervous investors. The price fell by over 10 per cent yesterday, although it has recovered today.