Lawyers representing both sides in the appeal against the EC's (European Commission's) 2004 Microsoft antitrust ruling were left fumbling today under cross-examination by one of the 13 judges hearing arguments.

Microsoft's appeal against the ruling is being heard in the Court of First Instance, Europe's second-highest court. Judge John Cooke initially turned to Microsoft lawyers, asking them about the information being sought by the EC to ensure that server software made by rival companies can work in a stack with Microsoft's Windows Server software.

"The suggestion by the EC is that Microsoft is exaggerating the extent of the remedy. Is this Microsoft's stance?" Cooke asked. His question temporarily left Microsoft lawyer Ian Forrester speechless. Forrester, who is Microsoft's top advocate on the issue of interoperability, has so far in the appeals hearing proved himself to be particularly eloquent, so his silence was all the more striking.

Cooke came to Forrester's aid, rephrasing the question: "Are you offering to disclose algorithms in order to show that what the EC is asking is impossible?" Forrester answered in the affirmative, adding swiftly that he denies that Microsoft has exaggerated the EC's demands.

Among the 13 judges, Cooke has proved to be by far the most knowledgeable about technology. After questioning Forrester, he turned to the EC, questioning the assertion made yesterday that Microsoft's trade secrets are of little value.

"These are not just trivial trade secrets. This is hugely valuable information developed by a major corporation taking hundreds of man-hours to develop," Cooke said. He added that he found it hard to follow the EC's logic in defence of its 2004 ruling.

It was then Anthony Whelan's turn to be rendered speechless. Whelan, one of the EC's lawyers on interoperability, composed himself after a few seconds and agreed that the information sought is strategically important.

Cooke's cross-examination does not necessarily reveal his thinking, representatives from both sides said after the court adjourned for lunch.

"The judge was just being provocative," said Thomas Vinje, a lawyer representing the European Committee for Interoperable Systems, a trade group and one of the EC's key allies in the case.

Microsoft's general counsel for Europe agreed. "It's not possible to predict from the questions what the outcome will be," said Horacio Gutierrez. He added that Cooke in particular has shown "a tremendous grasp of the economic, technical and legal arguments".