The Windows Genuine Advantage 1.0 programme aims to ensure that customers using Windows Update, Microsoft Update for Windows and the Microsoft Download Centre run a program that checks that their Windows operating system (OS) is genuine before they can download updates or new content from those services, says David Lazar, director of Genuine Windows for Microsoft.

The Redmond, Washington-based company has been testing the programme since September, and has validated more than 48m systems so far, Lazar says. Until today the programme was voluntary.

Customers who discover they have a counterfeit copy of Windows through the programme will either be given a free version of the OS, or can purchase it for a discounted price, he says.

To get a free version of Windows, a customer must fill out a counterfeit report identifying the source of the software, provide a proof of purchase and send in a counterfeit CD of the software.

If customers do not have all of that information, they can still fill out a counterfeit report, and receive a copy of Windows XP Home Edition for $99 or a copy of Windows XP Professional Edition for $149, Lazar says. Windows XP Home normally sells for $199 and Windows XP Professional Edition usually costs $299.

The move to lock out pirated copies of Windows from the download sites is part of Microsoft's effort to fight software piracy, which is a major issue for the software vendor.

Bonnie MacNaughton, senior attorney in the legal and corporate affairs department of Microsoft, says that the company estimates that more than one-third of all copies of its software are counterfeit, based on a recent joint report released by the Business Software Alliance and research firm IDC.

The study found that 35% of software worldwide is pirated. In North America alone, the piracy rate for software is 22%. "We consider that to be a staggering number," MacNaughton says.

One issue the software maker faces in fighting piracy is that many users do not know that their copy of Windows is illegal. Windows Genuine Advantage allows customers to solve this problem in a few minutes through the automatic validation, Lazar says.

The Windows Genuine Advantage checking mechanism is anonymous, and includes an ActiveX control on the client side and the Windows Product Activation service on the Microsoft side.

During the testing process, a user had to install the ActiveX control and enter the Windows product key, which on new PCs bought with the operating system is typically found on a sticker affixed to the PC. However, providing a Windows product key is no longer required in the live programme, Lazar adds.

This is not the first time that Microsoft is checking whether installed copies of Windows are legitimate. Windows Update already checks for certain volume licence keys that are known to be used illegally to activate copies of Windows.

Microsoft also has a Web site, http://www.howtotell.com, providing customers with information on how they can discover whether or not they have a genuine copy of Windows, Lazar says.

While counterfeit copies of Windows will be prevented from downloading updates, Lazar says that Microsoft is not including security updates in the lock-out.

Even customers who do not check their copies of Windows for authenticity will be allowed to download security updates through Windows Update, Microsoft Update for Windows and the Download Centre, he says.

"Those are available to all Windows users with or without validation," Lazar adds. "We think of it like public health. We want to make sure no one gets infected by another system on the Internet because of our programme."