Microsoft is continuing to cock-a-snook at US authorities, threatening to overrun an anti-trust deadline and promising only to make vital information available in a rights-protected file format.

Following protests about its behaviour, Microsoft has said it will review the format and suggest alternatives within 60 days. The MHT format - an HTML archiving tool that only works with Microsoft's own Explorer browser - cannot be searched or indexed, thereby making the process of understanding Microsoft's prioprietary protocols several magnitudes harder.

This obstructive behaviour was revealed in a joint status report by US Department of Justice, 16 states and the District of Columbia - the plaintiffs in the government's anti-trust case against Microsoft. The report is one of a series requested regularly by the District of Columbia to monitor Microsoft's compliance with the final judgment in the anti-trust case. The judgment requires Microsoft to document and license its software communications protocols, and to revise the terms under which it licenses Windows to PC makers, among other things.

In July, Microsoft said it would complete revisions of the documentation required by the court in the autumn - a season generally assumed to comprise the months of September, October and November. Microsoft has now said it may have to extend work on a beta or test version of the new documentation into December.

The plaintiffs have three main areas of concern about the documentation.

First is that Microsoft, asked to open up and document the interfaces to its communication protocols for licensees, has chosen to issue the documentation in the rights-protected MHT format, readable only in Explorer. This means licensees can neither annotate nor effectively search the information.

Microsoft defended its choice, saying it had put "very substantial effort" into converting all the documentation into MHT format because it can handle large documents and can secure the documentation. Microsoft said that it has published the specification for MHT and that it offers a free software development toolkit for the digital rights management system, enabling anyone to develop a new software application to decode and read the files using another browser.

Secondly, the plaintiffs questioned the completeness and accuracy of the documentation, saying that it was of the utmost importance that Microsoft address the issue over the next 60 days.

And finally, the plaintiffs highlighted the complex and error-prone system for distributing the documentation over the Internet. Microsoft has agreed to send the documentation to licensees on CD or DVD, it said.