(Tamoor Hussain @ CVG UK) The figure represents cumulative sales of Windows 8 including upgrades and sales to original equipment manufacturers for new devices.

Windows Blue update due later this year in response to customer feedback.

The operating system was released to manufacturing on August 1, 2012, and to the general public on October 26, 2012.

Speaking in a blog post on the official Windows website, Microsoft's chief marketing and financial officer Tami Reller said of the 100 million sales milestone:

"This is up from the 60 million license number we provided in January. We've also seen the number of certified devices for Windows 8 and Window RT grow to 2,400 devices, and we're seeing more and more touch devices in the mix."

Reller also confirmed that a new update, codenamed Windows Blue, will be available later this year.

"It will deliver the latest new innovations across an increasingly broad array of form factors of all sizes, display, battery life and performance, while creating new opportunities for our ecosystem," she said.

"It will provide more options for businesses, and give consumers more options for work and play. The Windows Blue update is also an opportunity for us to respond to the customer feedback that we've been closely listening to since the launch of Windows 8 and Windows RT."