The defendants are located in Arizona, Connecticut, Florida, Hawaii, Massachusetts, Nebraska, New York and Washington.
Microsoft traced seven of the alleged pirates through its Windows Genuine Advantage programme which allows users to check the validity of their software online. Several of the defendants were also reported through Microsoft's Anti-Piracy Hotline.
Microsoft claims that it actively monitors eBay and other auction sites for pirated software, and requested the removal of 50,000 listings last year.
The vendor unveiled a new anti-piracy programme last week which seeks to further emphasise the security risks of purchasing illegal software.
Copied software in some cases comes bundled with spyware or other malware, and in other cases credit card theft rings masquerade behind online stores promising discounted software.
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