Microsoft returned to court yesterday as the US government sought to prove that the software giant repeatedly abused its monopoly power to protect Windows, its flagship operating system.

Microsoft accused the government of attempting to "ambush" it by broadening the case just three weeks before the case is scheduled to go to trial.

In a volley of legal manoeuvres, Microsoft demanded that the issues in the trial be limited to those originally raised by the US government and 20 states when they filed their lawsuits in May.