Another VMware spokesman said the company won't say exactly how much market share it believes it has, saying "we don't publicly comment on market share." The spokesman questioned the IDC survey, though, saying a pool of 2,500 respondents may not be a representative sample. VMware has more than 120,000 customers. The spokesman also said the idea that Hyper-V gained significant market share after only being available a few days during the second quarter is "questionable."

VMware better-than-expected financial results in the third quarter this week, with revenue 32% higher than last year's period. VMware CEO Paul Maritz announced a hiring freeze and other changes to help VMware survive the economic downturn, but he also dismissed the notion that VMware is losing any substantial market share to rival Microsoft.

"We did not see any major losses to Microsoft," Maritz said, according to a of the third quarter earnings conference call. "Currently we take Microsoft very seriously and keep our eyes very closely focused on them. ... Despite the series of announcements over the last quarter, Microsoft is still behind in terms of their product roadmap and we do not see them catching up to us until the next 12 to 24 months."

When market share is counted by revenue, there is no contest between Microsoft and VMware. Microsoft, whose virtualization products are free or almost-free, has 1.1% of revenue share and VMware has 78%, according to IDC.