Microsoft is still using its old anti-competitive tricks to gain market share, according to European competition commissioner Neelie Kroes.

It is "unacceptable" that Microsoft continues to gain market share using tactics that were outlawed in the Commission's 2004 anti trust ruling, Kroes told European parliamentarians today.

Three years on Microsoft still has not complied with the main demand imposed by the European anti trust ruling: that the company share interoperability information inside Windows at a reasonable price to allow rival makers of workgroup servers to build products that work properly with PCs running Windows.

"Microsoft is constantly gaining market share and that is what is worrying in the workgroup server operating market," Kroes said. She told the parliamentarians that Microsoft's market share in this sector has continued to rise since the 2004 anti trust ruling. When the Commission began its anti trust investigation in 1999 Microsoft held between 35 percent and 40 percent market share. By 2004 it rose to around 60 percent and now it stands at between 70 percent and 75 percent.

"That's unacceptable," Kroes said.

Withholding the interoperability information is an illegal competitive tactic, the Commission said in 2004.

This unfair advantage would eventually result in Microsoft taking over the workgroup server market, the Commission predicted at the time of the ruling. The latest server market share figures appear to confirm that analysis.

Microsoft has repeatedly promised to comply with the 2004 ruling, even though it has appealed the decision to the European Court of First Instance in Luxembourg.

The software vendor has submitted documents but so far these have been deemed incomplete by the Commission and by an independent expert, picked by Microsoft and the Commission to oversee the company's compliance with the 2004 ruling.

Last July the Commission fined Microsoft £190m for failing to provide the interoperability information. This was in addition to the £337m fine that accompanied the 2004 ruling.

At the beginning of this month the Commission threatened further fines, accusing Microsoft of continuing to flout the ruling by failing to offer the necessary interoperability information "on reasonable and non-discriminatory terms."

Microsoft claims the prices for access to the interoperability information are justified because the information comes from its own innovative work and much of it is protected by patents.

However, the Commission said nearly all the information submitted is old and much of it is available royalty-free from other software vendors.