Unauthorized Windows 95 Andrew Schulman IDG Books, £39.99
A US federal court judge is considering an investigation into claims that Microsoft, the world`s leading PC software company, lures customers from rivals by announcing products before they are ready.

This claim is one of many complaints made about Microsoft. But until the judge's announcement, the problems had seemed to be settled: the powerful Seattle firm had negotiated a compromise with the US Department of Justice that allowed an anti-trust case to be halted.

If the case is reopened, much of the credit should go to a technical author, Andrew Schulman, who is like a Victorian explorer seeking the Yeti. Using an ingenious collection of home-spun programs, he probes the murky depths of system software.

He used this technique in his previous books Undocumented DOS and Undocumented Windows to reveal secret parts of programs that Microsoft used to its own advantage, helping its programmers to use shortcuts to develop applications such as word processors and spreadsheets, while laying booby traps for competitors. The revelations in his new book, Unauthorized Windows 95, have made an impact far beyond its specialist technical audience.

Schulman's new book will cause the world's most efficient marketing organisation acute embarrassment. It reveals a campaign of disinformation that apparently suckered many of Microsoft's own marketing people, as well as - in his words - "the supposedly independent oversight of an easily confused, cajoled and hoodwinked trade press".

The story goes like this. Having conquered the computing desktop with Windows, a system widely seen as technically inadequate, Microsoft wants its next release to silence the sceptics. So it informs the world that a miracle is imminent: a brand-new system, Windows 95, which looks and feels beautiful, and is "32-bit" - ie, it can address far more memory addresses than the traditional 8 bits of a PC. This makes it as grown- up as such operating systems as Unix or VMS, which are used to power minicomputers and mainframes. The jump from 8 to 32 bits is like the leap from steam turbine to jet propulsion.

Schulman found that many of Microsoft's claims for Windows 95 since it was first announced were unfounded. The system uses DOS, or DOS-like code, continually. And it's far from being all 32-bit. Not only is much of it derived from Microsoft's existing systems, but much is not new at all; it is already in use in Windows 3.1, in source code labelled "prototype".

The author has no ideological axe to grind with Microsoft. He recognises the commercial imperative behind its "sensible compromises", and eschews the attacks on Windows 95 by partisan operating system fanatics as silly stuff. Instead, he writes, "what's unreasonable is Microsoft's denials".

These are serious allegations. As corporations downsize or upgrade their systems, whose software should they choose? There are plenty of choices, notably IBM's OS/2 Warp and the new Mac operating systems, which fulfil the macho credentials claimed for Windows 95. But Windows 95 remains "vapourware" - software that is promised but not yet a reality. Should they wait? Billions of dollars worldwide await such purchasing decisions.

Schulman's conclusion is one that the judge will doubtless note. In his view, we should stop thinking of Microsoft as the shark, and accept that it now constitutes the pond.