Microsoft is suing eight computer system builders and resellers in seven US states after accusing them of distributing counterfeit and unlicensed software and components.
The lawsuits follow similar action at the end of last year against eight dealers.
Microsoft said its legal action was partly in response to complaints from resellers who are operating legitimately, and who complained about alleged illegal sales that were harming their business.
The lawsuits have been filed against firms in California, Texas, Florida, New Jersey, Alabama, Maryland and Rhode Island.
The Business Software Alliance claims 22% of software being used on US PCs is unlicensed or counterfeit.