Microsoft filed federal copyright infringement lawsuits Monday against about 30 companies nationwide, including a computer dealer in Panhandle, alleging the companies illegally sold or distributed counterfeit copies of the company's software.

The suits were filed in 25 cities across the United States from Riverbank, Calif., to Melbourne, Fla., and were aimed at companies that allegedly distributed counterfeit software or installed unlicensed software on computers they sold.

The suit against Panhandle Computer Services alleges that Russell Offringa, owner of Panhandle Computer Services, knowingly sold computers loaded with purported Windows XP Pro software to an investigator in July and August, infringing on Microsoft's registered copyrights.

Offringa did not immediately return a phone call Monday from the Globe-News seeking comment on the suit.

In Texas, similar suits were filed against companies in Wichita Falls, Houston, Humble and Rowlett, Microsoft said.

Mary Jo Schrade, a senior attorney at Microsoft, said the company uncovered the alleged copyright infringement by having secret shoppers scope out computer companies across the country.

"These are all companies that we actually went out and actually purchased from them either software or computers and they were infringing, either counterfeit software or what we call hard-disk loaded software, which is where you take one copy of Windows and you basically load it on every computer you sell," she said.

Schrade said Microsoft warned the companies sued Monday to halt practices it said infringed on Microsoft's copyrights and is seeking unspecified damages from the defendants.

Counterfeiters must physically alter the software's code to bypass Microsoft's installation and licensing protections.

Sometimes, essential portions of programs are deleted and unnecessary coding is added.

Deleting software coding can cause software to fail to work with other software or devices. Extra coding inserted by counterfeiters can infect a PC with viruses, change settings or even track keystrokes.

Such software can be used to steal usernames, passwords and credit card numbers, Microsoft said.

"No consumer has the ability to examine the code that a counterfeiter has offered for sale, so there's no way to tell how it's been altered until it's too late," said Laura Didio, an analyst with Yankee Group, a technology consulting firm.

Schrade said consumers can go online and check to ensure that the software in their computers is legitimate at Microsoft.com/genuine.