Microsoft has launched a legal blitz against software pirates in California and Florida with the filing of 23 lawsuits against merchants which it claims are selling counterfeit software.

The latest filings bring Microsoft's total number of legal actions to 125 during the past year.

The company claims that it is helping to protect honest system builders and resellers which find it difficult to compete against companies selling pirated software.

Mary Jo Schrade, senior attorney at Microsoft, said: "Whether customers buy a new computer or software from a large retail chain or an independent business in their neighbourhood, we want them to feel confident that they will have the security and support they need when using our product."

The actions follow the formation of a bipartisan group of Federal lawmakers to work against software piracy.

The Congressional International Anti-Piracy Caucus, formed in 2003, comprises 70 members who are particularly focused on the global reach of the problem.

"A large sector of the US economy is dedicated to the production and sale of copyrighted material, and this sector is at great risk due to the unauthorised reproduction and distribution of these materials around the world," said California Congressman Adam B. Schiff, a co-chairman of the caucus.

"The continued reduction of software piracy will increase revenues and help to create more jobs, resulting in a much stronger US economy."

Software piracy cost the US economy around $7.3bn in revenues in 2006, according to a study conducted by industry analyst firm IDC and commissioned by the Business Software Alliance.