The European Commission has given a guarded welcome to Microsoft's offer of "greater transparency" in its business.

Microsoft's promise to open up more APIs to proprietary software products and let developers build open-source implementations using them wouldn't stop the EC from taking further anti-trust action against the vendor for monopoly abuse that has occurred up to now.

The EC also said that Microsoft has in the past made statements on the importance of interoperability, which amounted to nothing. On Thursday, Microsoft said the expanded software access would include some of its major software products, including Windows and Office.

"This announcement does not relate to the question of whether or not Microsoft has been complying with EU anti-trust rules in this area in the past," the Commission said.

The Commission, the European Union's top anti-trust regulator, opened two new anti-trust investigations of Microsoft's activities last month, based on the same legal principles that underpinned its landmark 2004 ruling against the company.

One case is looking into claims that Microsoft is abusing the dominance of its Office software package by failing to provide interoperability information to rivals. The other is examining whether the company is unfairly giving its Internet browser an advantage over rival browsers by tying it to the Windows operating system.

The Commission said it would examine whether the new changes announced by Microsoft are actually made, and whether they would end the interoperability infringement that lies at the heart of the first new case.

However, the announcement won't affect the second new case concerning the tying of Internet Explorer to Windows, the Commission said.

The Commission's scepticism about Microsoft's latest pledge to compete fairly comes after "at least four similar statements by Microsoft on the importance of interoperability," the Commission said.

ECIS, the European Committee for Interoperable Systems, voiced similar scepticism.

"The proof of this pudding will be in the eating. The world needs a permanent change in Microsoft’s behaviour, not just another announcement. We have heard high-profile commitments from Microsoft a half-dozen times over the past two years, but have yet to see any lasting change in Microsoft’s behaviour in the marketplace," said ECIS.

ECIS filed a complaint to the Commission that sparked the latest probe into Office. One of its members, the Norwegian Internet browser vendor Opera, filed the complaint that sparked the investigation into the tying of Internet Explorer to Windows.

Microsoft's statement raises more questions than it answers, ECIS said. "Microsoft promises not to sue open source developers for 'non-commercial distribution.' That's presumably great news for hobbyists, but completely excludes some of Microsoft’s most threatening potential competitors," ECIS said.

Microsoft's commitment to "enhancing support for industry standards" prompted ECIS to ask: "Whose standards? For years now, Microsoft has either failed to implement or has actively corrupted a range of truly open standards adopted and implemented by the rest of the industry. Unless and until that behaviour stops, today's words mean nothing."