Microsoft has sued four online retailers in California and Virginia for selling pirated software, the world's largest software maker said on Wednesday.

Microsoft said it had received complaints from consumers and businesses who had purchased software from CEO Microsystems and Wiston Group in California. In Virginia, Microsoft sued #9 Software, East Outlet and Super Supplier. The Wiston Group said its president, Wenchi Ri, was not available for comment, and a representative from #9 Software declined to comment.

Messages left at East Outlet and Super Supplier were not returned while CEO Microsystems was not immediately available for comment. Redmond, Washington-based Microsoft said the companies had sold pirated copies of its Windows XP, Windows Server and SQL Server software.

Bonnie MacNaughton, senior attorney at Microsoft, said the defendants were sent cease-and-desist orders and Microsoft waited weeks or months before the lawsuits were filed. "Shutting down people who engage in piracy is our priority," said MacNaughton.

Microsoft, which said it was seeking more than $1 million from each retailer, filed its lawsuits in the US District Court for the Eastern District of Virginia and the US District Court for the Central District of California.

Microsoft said it began investigating the complaints from customers who had bought software from the stores and tried to register it, unsuccessfully. In the case of #9 Software, Microsoft also said the company had violated a federal statute passed last year that prohibits the improper use of a certificate of authenticity label.

Microsoft has filed lawsuits against other companies in the US and other countries, including China, for selling pirated software.