The company said the new OS is outpacing Windows 7 in terms of upgrades
Software maker Microsoft has sold 40 million Windows 8 operating system (OS) licenses in the first month since its launch on 26 October this year.
Microsoft finance and marketing head of the Windows business Tami Reller said: "Windows 8 is outpacing Windows 7 in terms of upgrades. We built Windows 8 to work great on existing Windows 7 PCs."
"And we also set out to make upgrading from Windows 7 to Windows 8 super easy," Reller said.
Microsoft had sold just more than 60 million copies of Windows 7 in its first two months since its launch in October 2009.
In October this year, Microsoft CEO Steve Ballmer had said that the company sold four million upgrades to Windows 8 OS in the first four days.
Windows 8, which is designed to compete with Apple's iOS products such as the iPad, is available as Windows 8 Pro and Windows 8 Enterprise, for larger organisations.
Critics say that the new OS is too drastic from its previous versions and is confusing to use and some experts say the radical change is risky as Microsoft could lose faithful users of its previous versions.
Apart from Windows 8, Microsoft said it had sold over 750,000 Xbox game consoles in the US last week.