Microsoft is trying to make pirated software less attractive by offering free and discounted software to legitimate users.

Windows Genuine Advantage has been in pilot for 10 months and is now being rolled out for Windows 2000 and XP customers. 

On entering the Windows Update site users will be asked to download an ActiveX routine that checks to see whether their code is legitimate before allowing access.

Members of the programme will get free software that Microsoft values at £280 as well as discounts on software and trials of applications.

"The principle is that we offer things to genuine customers, encouraging users to ask for genuine software," said Alex Hilton, anti-piracy manager at Microsoft UK.

However, those using pirated software will not be blocked from security updates. Hilton explained that this is to avoid the creation of a reservoir of unpatched systems that could cause security problems.