Microsoft has kicked off an "unprecedented" assault against software pirates with a coordinated campaign of 26 separate legal actions filed against alleged copyright criminals across the US.

The actions include suits against companies that allegedly pirated software or participated in hard-disk loading (installing unlicensed software on computers they sold).

One of the lawsuits was filed against a reseller in Georgia who was recently indicted on federal criminal charges. Lawsuits were filed in Colorado, Georgia, Illinois, New Jersey, New York, Ohio and South Carolina.

"Our message should be made very clear by today's lawsuits," said Mary Jo Schrade, senior attorney at Microsoft.

"To our honest partners, and to consumers who expect and should receive genuine Microsoft software wherever they go to buy it, we are listening and we are investing a tremendous amount of resources to help you.

"We are committed to finding the unscrupulous dealers of pirated software and making piracy a business model that doesn't work."

Microsoft gathered evidence for the cases through the deployment of a programme akin to a 'secret shopper' concept.

As part of its test purchase scheme, the company buys hardware and software from computer dealers across the country and then tests the software and software components to determine their authenticity.

In many of the cases, Microsoft notified defendants of the illegal activity and provided information on how the dealer could acquire and distribute genuine software.

Complaints were also received about some of the defendants through the Microsoft anti-piracy hotline.

According to the Business Software Alliance, 21 per cent of all software in the US is pirated.