FORT LAUDERDALE, Fla. — Microsoft Corp. last week filed 16 federal lawsuits against people or companies based in the United States suspected of selling knock-off software through online auction sites.

In addition, the Redmond, Wash.-based company initiated criminal and/or civil actions in 11 other countries, including New Zealand, Japan and the Dominican Republic.

Microsoft's wave of legal actions highlights the need for people to be vigilant when they are shopping online for software, said Matt Lundy, the company's senior attorney for its anti-piracy effort.

This is the third consecutive holiday season Microsoft has gone after suspected sellers of counterfeit software. Counterfeit software can leave buyers vulnerable to data loss, identity theft and viruses.

"It's analogous to operating a car with defective brakes," Lundy said. "You're taking a risk every time you get in your vehicle."

In particular, Microsoft has seen a proliferation in counterfeit software marketed as "Blue Edition" software, which online auctioneers claim can be bought cheaply because it's part of an overrun.

Among those facing a civil lawsuit is Miami resident Gabriel Lagoa and his company, Computer Doctor of Miami.

Lagoa said he's stumped as to why Microsoft filed a lawsuit against him in federal court in Seattle. The software sold by Computer Doctor of Miami mostly is bought from other online resellers, he said.

"Maybe they sold me nonlegitimate software," Lagoa said.

Microsoft alleges that its investigators bought a counterfeit version of Microsoft Office 2003 from Lagoa's company through an Internet auction site. Microsoft sent a cease-and-desist letter to the Miami company, but it continued selling counterfeit software, according to the lawsuit.

Microsoft is asking for a court order to ban Computer Doctor of Miami from selling counterfeit software as well as an unspecified amount in monetary damages.

Lagoa maintains he has never been contacted by Microsoft.

"I'm shocked, but at this point I don't think I should say anything further," he said. "I had no idea of any of this."