From today, only Windows Vista users that have installed Service Pack 1 or above will be eligible for support for the operating system from Microsoft.

The support means PC users will continue to receive updates that Microsoft said would focus "on system reliability, program compatibility and security".

The company is urging those that do not have SP1 or above installed to either upgrade to its latest operating system, Windows 7, or failing that, to download and install Service Pack 2, which is the latest service pack for Vista.

Windows 7 was launched in October last year. According to web analytics firm, Net Applications, Microsoft's latest OS is already being used on 10 percent of PCs worldwide.

It can be downloaded for free from Microsoft's dedicated web page.

See also: Windows 7 is Microsoft's fastest-selling OS