Since January, several rivals, including Mozilla and Google -- the latter because of its Chrome browser -- as third-party participants. Several weeks ago, a trade group that includes other competitors, among them Adobe, IBM and Oracle, were also given access to the allegations.

Although EU regulators have not spelled out what they may demand of Microsoft, the agency has hinted it could fine the company, force it to allow users to choose alternate browsers or require it to disable IE.

Opera wants the commission to make Microsoft offer alternate browsers using the same Windows Update service the latter relies on to upgrade IE. "That's one possible remedy," said Lie, who called it a "must-carry" solution, meaning Windows would have to provide multiple browsers, not just IE.

In Lie's scenario, Windows Update would offer a number of choices as optional downloads by providing small executables that would in turn download and install Firefox, Chrome, Opera or other browsers. "Or Windows Update could pre-fetch all those browsers," Lie said, and have them ready to install when the user chooses which browser to run.

"We've suggested this to the EU," Lie confirmed.