Most of the companies sued are small, independent dealers or Internet merchants carrying non-descript names such as ABC Rentals & Computers, The Computer Guy, and Best Price Computers.
Other vendors sued by Microsoft include Computer America, Bisdex, Ben's Hobby Computers, and Cyber Cycle.
Microsoft is accusing the defendants of selling bootleg CDs containing its software or shipping computers with illegitimate copies of Windows installed. The software is usually sold at prices well below those offered by legitimate sellers, Microsoft said.
The lawsuits are part of Microsoft's "three-pronged" effort to reduce software piracy, which the company said costs the U.S. economy $7.3 billion per year. "The negative impact of piracy is further reaching than most can imagine," said Rep Michael McCaul, R-Texas, in a statement provided by Microsoft.
In addition to the court actions, Microsoft has set up a Web site -- Howtotell.com -- designed to help consumers detect fake software.
The third part of Microsoft's war against software pirates involves product engineering solutions, such as Windows Genuine Advantage, that help ensure that only legitimately purchased copies of Microsoft products are installed on users' PCs.
Not all of those efforts have gone smoothly, however. Microsoft itself has been sued by computer users who claim that Windows Genuine Advantage improperly identified them as software pirates. Microsoft officials have countered such claims, suggesting the false positive rate for WGA is less than one half of 1%.