Microsoft has sold 40 million Windows 8 licences since its launch last month.

The software giant says sales of the operating system eclipse that of Windows 7 three years ago, representing a solid start for the product.

While the company did not offer an exact comparison, finance and marketing head of Windows Tami Reller suggested sales were ahead of the previous system, which shifted 60 million units during the first ten weeks of sale in 2009.

"Windows 8 upgrade momentum is outpacing that of Windows 7," Reller said.

The news comes less than ten days after Microsoft CEO Steve Ballmer publicly criticised rivals Apple and Android, branding them expensive and wild respectively.

Speaking to LinkedIn founder Reid Hoffman, Ballmer also claimed Microsoft’s new release would fit perfectly in the marketplace but would not command the entire industry.

“The question is how do you get the quality with maybe not the premium price of the phone, with maybe not quite as controlled an ecosystem,” he said.

“Apple’s system looks highly controlled and quite high prices.

“And how do you allow for the lower price points, more affordability, diversity that comes with Android.

“The ecosystem of Android is a little wild.

“And I think you can say that’s kind of the best of both worlds and that’s available to us.”

Of the 40 million upgrades however, many of the sales are attributed to PC manufactures with research firm StatCounter claiming around 1% of the world's 1.5 billion PCs - equating to 15 million - are actually running Windows 8.

While discussing the sales, Reller also said the Windows team was doing well after Steven Sinofsky's recent departure.

"The team holistically is in great, great shape," Reller said.

"And the product is in great shape.

"I think transitions are always somewhat of a challenge, but I think that timing-wise it is a reasonable time, and the team is busy."

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