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When SCO Group filed a $1 billion suit against IBM in March 2003, it was widely interpreted as a final gambit to try to persuade the systems giant to buy the ailing company.

And when SCO CEO Darl McBride started firing off letters to hundreds of major companies warning them that "Linux infringes on our Unix intellectual property and other rights" and that they faced "legal liability", it was clear that SCO meant business.

It seems likely that the case will go to court - and the consequences of a SCO win have clearly spooked open source software advocates. "A judgement in favour of SCO could do serious damage to the open source community. SCO's implication of wider claims could turn Linux into an intellectual property minefield, with potential users... wary of being mugged by previously unasserted IP claims," open source advocate Eric Raymond wrote in a paper for the Open Source Initiative.

SCO's claims are manifold. First, it suggests that IBM has not stuck to the letter of its Unix licensing agreement, signed way back in 1985, which obligates IBM to maintain the confidentiality of the original Unix software code on which AIX 1.0 was based.

Second, SCO claims that the Linux kernel is riddled with code taken directly from SCO's own UnixWare product.

Third, SCO claims that IBM misappropriated technology developed when the two companies were engaged in Monterey, a joint project to create a unified 64-bit Unix for Intel's Itanium microprocessor. That technology, he claims, found its way into Linux after IBM dumped Monterey and SCO in 2001.

Will SCO win?

The question that all Linux vendors and users are now asking is, will SCO win?

SCO's first claim has already been put to the scrutiny of the US courts and been found wanting. In 1993, the-then owner of the Unix source code, AT&T, took the University of California at Berkeley to court alleging copyright infringement in version 4.4 of Berkeley's BSD open source Unix. AT&T was humiliated. Just three out of the 18,000 files in the distribution were considered the property of AT&T and they were easily removed. "The rest were ruled to be freely re-distributable," says Raymond.

SCO's second claim has also been derided in the open source community. "AIX engineers don't even give Linux engineers the time of day, let alone even let them so much as sneak a peak at the AIX code," says one.

Others say that IBM has been very diligent about establishing various controls, such as 'Chinese walls' between Linux and AIX developers, to prevent any kind of code contamination from taking place.

In a June 2002 interview with online magazine Slashdot, IBM Linux developer Dave Hansen said: "Before any of us were allowed to contribute to Linux, we were required to take an 'open source developers' class... We are definitely not allowed to cut and paste proprietary code into any open source projects (or vice versa)."

Perhaps most damaging to the SCO case, however, is that Novell, the company that sold it the rights to various Unix products in 1995, says that it continues to hold the key Unix patents.

"Contrary to SCO's assertions, SCO is not the owner of the Unix copyrights... a review of the asset transfer agreement between Novell and SCO confirms it," wrote Jack Messman, Novell's CEO in an open letter to McBride. Novell, moreover, says it will not be seeking recourse against the open source community.

And then there is the matter of the Linux general public licence (GPL). Until 15 May 2003, SCO was a Linux distributor itself. So even if the Linux kernel did contain any proprietary SCO technology, SCO distributed it under the GPL, effectively open sourcing the very technology over which it is now suing IBM.

While all these factors undermine SCO's case, the fracas has unsettled users. The real winner then could be Microsoft, as companies opt to stick with Windows rather than embrace Linux.