Microsoft has sold 60 million licences of its Windows 8 operating system, the software giant announced yesterday.

The figure was announced by Tami Reller, Microsoft’s Windows chief marketing officer and chief financial officer, at the Consumer Electronics Show (CES) in Las Vegas on Tuesday.

In an offical blog post, the company claimed that sales of Windows 8, which was launched in October, have so far been in line with uptake of its previous operating system, Windows 7.

This claim was made by comparing the average monthly sales for the first two and half months of Windows 8’s availability (c. 24 million) with the monthly average for Windows 7’s first nine months (19,4 million).

However, Microsoft previously revealed that it sold 40 million Windows 8 licences in the first month of its availability, meaning that it has sold 20 million in the last month and a half. That means that the current monthly average is 13.3 million licenses.

Microsoft also said that it had seen a "significant increase" in the number of Windows 8 certified systems since October, which now total over 1,700, and that it has attracted more developers to the Windows 8 application store.

"This week we also highlighted strong growth in developers building for Windows 8," Microsoft wrote in its blog post. "Since the opening of the Windows Store the number of apps has quadrupled and we passed the 100 million app download mark – just two months after general availability."

The success of Windows 8 is being watched especially keenly as it seen as a make or break opportunity for Microsoft to hold onto its historically dominant but much threatened position in the operating system market.

According to news agency Reuters, Microsoft’s shares fell 0.5% to $26.55 on the Nasdaq stock exchange after the announcement.