Google has issued its clearest challenge to rival Microsoft so far, by announcing its plans to create a new computer operating system aimed at laptop users.

The Californian internet company said it is working on a lightweight system that is based on the Chrome web browser it launched last year.

“It’s our attempt to re-think what operating systems should be,” said the company on the Official Google Blog.

The first version of the system, which will be targeted at netbook computers – the small, portable laptops that have become popular in recent years – is due to be made available in the second half of 2010.

“Speed, simplicity and security are the key aspects of Google Chrome OS,” said the announcement. “We’re designing the OS to be fast and lightweight, to start up and get you onto the web in a few seconds. The user interface is minimal to stay out of your way, and most of the user experience takes place on the web.”

It added that there would be a heavy focus on creating a system that would not require users to worry about security holes and virus warnings.

“As we did for the Google Chrome browser, we are going back to the basics and completely redesigning the underlying security architecture of the OS so that users don’t have to deal with viruses, malware and security updates.”

Although the company was keen to keep expectations low by suggesting a focus on netbook computers, it will undoubtedly be hoping that it can make inroads against Microsoft, the software giant that has dominated the operating system market for more than a decade with Windows.

Although others have attempted to take on Microsoft over the years – with rival software such as Apple’s Macintosh OS as well as the open source Linux system – it has proved impossible to erode.

According to figures from Net Applications, Windows currently runs around 90% of computers worldwide, with Apple’s OSX trailing in second with 8%.

Speculation about the possibility of Google working on such a project has been rife around the hi-tech industry for some time – and the internet giant has made few attempts to hide its ambitious plans.

In 2007, the Silicon Valley giant said it would be creating a new system to run mobile phones called Android, which was installed on handsets for the first time last year.

The company has also rolled out a series of web-based office applications targeted at Microsoft’s popular Word and Excel products – but perhaps the biggest signal of Google’s ambitions came when the company launched Chrome last September, a move which surprised the technology industry as an attempt to gain a foothold in the highly competitive web browser market.

The Google Docs suite has made some progress since launch, but neither Android or Chrome have yet to make a significant impact on their respective markets – with only a handful of Android phones released and Chrome commanding just 2% of web browsers.