Continuing its worldwide assault on software piracy, Microsoft has filed 20 lawsuits against resellers accused of distributing unauthorised copies of its software.

The lawsuits, filed against 20 resellers in the US, accuse the companies of either distributing counterfeit software on CDs or installing it on PCs that are then sold to consumers and businesses, a practice known as hard-disk loading. The software maker filed the lawsuits in nine US states.

Microsoft also announced the results of its first large-scale forensic analysis of counterfeit versions of Windows acquired in 17 countries. The company found 34 per cent of the 348 counterfeit copies analysed could not be installed on computers, and 43 per cent contained additional programs that aren't part of Windows.

The legal actions and the forensic analysis are part of Microsoft's broader Genuine Software Initiative, a program to protect the company's intellectual property.

In 2005, Microsoft introduced Windows Genuine Advantage (WGA) as part of this initiative. WGA automatically checks that customers using Windows Update, Microsoft Update for Windows and the Microsoft Download Center have a legitimate version of Windows before they can download updates from those services.