Nine US states are taking legal action in a bid to force Microsoft to release the blueprints for its internet browser.
The states' lawyers told a judge that the blueprints must be released to create competition in a market Microsoft illegally dominates.
Brendan Sullivan, the lead attorney for the nine states, says the internet Explorer is the fruit of Microsoft's statutory violations. Mr Sullivan says forcing Microsoft to give up its blueprints for Explorer would provide "fertile ground" for competitors.
Lawyers for both sides gave opening statements in the first week of a hearing to determine what penalties Microsoft should face. An antitrust case has ruled that the company operates as an illegal monopoly.
US District Judge Colleen Kollar-Kotelly must decide whether to impose tougher penalties than those the federal government imposed in a settlement with the company last year.
The states want the company to release a new version of Windows in which Microsoft features can be removed.
Brad Smith, Microsoft's general counsel, says: "Third-party applications that rely on (the removed Windows software) will stop working as they're supposed to.
"It's going to create new security vulnerabilities in the Windows product because as people move code they're going to create holes in the software."
The proceedings are expected to last two months. The nine states still pursuing legal action against Microsoft are California, Connecticut, Florida, Iowa, Kansas, Massachusetts, Minnesota, Utah, West Virginia and the District of Columbia.
They plan to call some of Microsoft's fiercest rivals as witnesses to help make their case that harsher penalties are necessary to protect consumers and competitors.
Story filed: 16:38 Monday 18th March 2002