The US government is tracking development work on Microsoft's new OS, Longhorn, to make sure it doesn't violate the final judgement brought in its anti-trust case against the software giant.

The US Department of Justice (DoJ) and several US states involved in the case are particularly interested in any changes that Microsoft might make in Longhorn related to default settings and "middleware" such as its Web browser and media player software.

As part of the final judgment, Microsoft was told to make it easy for users and PC vendors to remove access to Microsoft middleware products and select competing products instead. Additionally, Windows can't be programmed to automatically change the configuration of icons, shortcuts or menu entries installed by a PC vendor.

"Early attention to these issues will enable plaintiffs and Microsoft to address any potential concerns in a timely matter, before the final structure of the product is locked into place," reads a joint status report on Microsoft's adherence to the final judgment, originally made in 2002.

Microsoft has provided the anti-trust authorities with information on the development of Longhorn and discussions about the future operating system release have begun, according to the filing. Longhorn is expected to be released in 2006, and a first beta of the product is slated for release in early 2005, Microsoft has said.

A technical committee for the DoJ and the states is also testing the upcoming Service Pack 2 for Windows XP for compliance with the final judgment. The work includes running hundreds of tests to check the behaviour of Windows in relation to third-party middleware products. Similar tests will be done with Longhorn, according to the filing.

The joint status report also discusses continuing issues regarding Microsoft's compliance, including the Microsoft Communications Protocol Program (MCPP) and Microsoft's licensing terms for PC vendors. The MCPP makes Microsoft's Windows communications protocols available to third parties. Microsoft started licensing its protocols through the program in August 2002, and the program has been revised several times since then in response to comments from the DoJ.

Microsoft is still working on simplifying the technical documentation associated with the MCPP, which it agreed to do in April after complaints were received by the DoJ. Microsoft is also expanding the MCPP program with technical support, according to Friday's filing.

Additionally, the DoJ and the settling states are now satisfied that Microsoft's removal of so-called "non-assert provisions" in the licences for PC sellers resolves any compliance concerns in that area. The provisions prevented licensees from suing Microsoft over patents related to Windows.

One remaining concern over the MCPP is that Sun still has not signed an agreement it made with Microsoft, the DoJ and the states wrote in Friday's filing. The agreement was announced on 1 April and Microsoft expects it to be signed later this month.