The Open Source Development Lab, home of the Linux kernel, has published a paper attacking the SCO Group's use of the GNU Public Licence (GPL) in its $3bn lawsuit against IBM.
In the paper SCO: Without Fear and Without Research, Eben Moglen, professor of law at Columbia University, claims that SCO uses the GPL when it suits, yet argues that the GPL is not valid.
"SCO's legal situation contains an inherent contradiction. IBM's counterclaim painted SCO into a corner on the subject of the GPL," he said.
"Not only the facts but also the law are now fundamentally against SCO's increasingly desperate position."
Professor Moglen said that SCO had "benefited enormously" from the protections of the GPL because it has distributed - and continues to distribute - Linux under GPL.
SCO's case against IBM is that it contributed "trade secrets" covered by non-disclosure licences or agreements to the Linux kernel.
But Moglen insisted that this means SCO "has therefore published its supposed trade secrets and copyrighted material under a licence that gives everyone permission to copy, modify and redistribute".
Blake Stowell, director of public relations at SCO, hit back. "Section 0 of the GPL specifically states: 'This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this GPL,'" he said.
"I would challenge anyone involved with the GPL to find a notice that has been placed by SCO indicating that the company's 32-bit Unix System V code may now be freely distributed within Linux OS. Such a notice does not exist."
Professor Moglen also took issue with two examples cited by SCO of apparent copying of code from Unix System V to Linux.
The first piece of disputed code implements the Berkeley Packet Filter firewall written by Linux developer Jay Schulist which, according to Moglen, was part of BSD Unix which was copied legally into Unix.
The second example was in Unix Version 3 from 1973 and formed part of the AT&T versus University of California at Berkeley litigation.
AT&T had failed to include copyright notices so, under pre-1976 law, it had put the code in the public domain, said Professor Moglen.
Microsoft receives a 30 per cent cut of all purchases on the Xbox digital store
Credit card thieves used Apple ID accounts to buy and sell virtual currency for Clash of Clans and Clash Royale and Marvel Contest of Champions
$5.1bn fine further evidence that the EU is anti-US, claims Trump
New cable will connect Virginia to France