Microsoft's claim to the word "Windows" suffered another blow this week when a federal judge again questioned the company's assertion that the term is not generic.

The judge also repeated his denial of Microsoft's request to shut down the Lindows.com site and block its owner from advertising its product.

Lindows, started by Michael Robertson, the founder and former CEO of MP3.com, aims to offer an alternative to Microsoft's dominant Windows operating system by selling a new program, LindowsOS, which would allow Windows programs to run on the Linux operating system. A legal battle has been ongoing in federal court in Seattle since December, when Microsoft sued the start-up to prevent use of the Lindows name, claiming it violated Microsoft's trademarks.

In a preliminary ruling in March, U.S. District Judge John Coughenour questioned whether the word "Windows" is entitled to trademark protection. He also denied the software giant's request to shutter Lindows' site.

Microsoft, fiercely protective of its Windows franchise, appealed the ruling, asking the judge to reconsider.

Coughenour on Tuesday reiterated his previous decision in a seven-page ruling, saying competitors and dictionary definitions demonstrated that the "consuming public used the terms 'windows,' 'window' and 'windowing' to indicate a general type of user interface." He said the term was generic in the same way that the words "light" in "light beer" and "matchbox" in "matchbox toys" are.

Coughenour also cited Microsoft's own use of the word "windowing" in its documentation as proof that the term is generic.

"Through its own use of the evidence, Microsoft essentially admits that these terms refer to the genus of computer software products that have windowing capability," he wrote.

The ruling is a setback for Microsoft's attempts to claim the Windows name as its own, and it could open the door for other companies to use the term in their products.

"This time their strategy has not only failed but has completely backfired," Lindows' Robertson said in a statement. "Microsoft's attempt to intimidate Lindows.com through legal attacks is part of their ongoing war waged against any potential competitor."

In a statement, Microsoft said it respectfully disagreed with the ruling and would continue to prepare for a trial.

"The Windows mark is a one of the most recognizable brands in the world, and we will defend the years of hard work that went into building it into a trusted name among consumers," the company said.

News.com's Lisa M. Bowman contributed to this report.