Microsoft has filed eight lawsuits accusing companies in Arizona, California, Illinois, Minnesota and New York of distributing counterfeit software.

According to the Redmond giant, the actions resulted from tip-offs by members of the public who reported suspicious software deals.

Some of the alleged offenders were nabbed by what Microsoft called "secret shoppers" who selectively purchase and test the authenticity of software being distributed in the marketplace.

Microsoft added that the lawsuit against MicroCity4Less.com (which also trades as Image & Business Solutions and Hi Tech Outlets, Estore, Gizmos2Go.com and EZ4U123.com) relied, in part, on evidence submitted by consumers through its Windows Genuine Advantage programme which was recently set up to ensnare software pirates.

Microsoft explained that it considers taking legal action against alleged software pirates to be "a last, but effective, resort". The company claims to file lawsuits only after other efforts to "warn and educate these companies" have failed.

"Microsoft does not take legal action lightly. We remain very serious about protecting honest software resellers and consumers from the illegal activities of software counterfeiters," said Mary Jo Schrade, senior attorney at Microsoft.

"It is very clear to us that our customers want to know if they've received the product they paid for, and it is gratifying to see that initiatives such as Windows Genuine Advantage, Microsoft's test purchase programme and the piracy hotline are proving to be successful in helping to address this widespread problem."

Each of the other lawsuits announced today relied on evidence gathered through Microsoft's test purchase programme, which the company uses to test the authenticity of software and software components purchased from resellers.

Two of the lawsuits were filed against businesses allegedly in violation of settlement agreements entered into with Microsoft.