Microsoft has angered some competitors by limiting the technical data it promised to release under the terms of its antitrust settlement.

The Redmond giant has claimed that the restrictions are normal for the software industry and do not violate the terms of the agreement.

But competitors have argued that Microsoft's actions are a return to the old days, which led to the antitrust case in the first place.

At the heart of the row is the wording of the settlement that requires Microsoft to release details about "communications protocols" that its products use to transfer information between its own and non-Microsoft products.

During the antitrust case, the company was accused of withholding such information to maintain a competitive advantage.

The settlement allows Microsoft to charge for the communications protocols, but demands that they must be distributed in reasonable and non-discriminatory terms.

In order to gain access, a company would have to use Microsoft's Passport identity authentication system, then request and sign two forms - one of them promising secrecy - just to see the licence terms and find how much Microsoft is charging for the information.

Linux seller Red Hat maintained that the process is offensive. Since Microsoft is charging a royalty fee to use the communications protocols, any open source company would not be able to use them.

A Red Hat spokesman told Associated Press that Microsoft is doing nothing to level the playing field.

But Microsoft stated that the protocol process is straightforward, arguing that non-disclosure agreements are common in the industry.