SCO has hit back at its critics, insisting that it - not Novell - owns the copyright to Unix.

The move is the latest in the skirmish begun by SCO with its threat to start an intellectual property war over Linux. The company claims that Linux illegally uses Unix code to which it holds the rights.

SCO maintains that all rights to the Unix and UnixWare technology, including copyrights, were transferred to SCO as part of an Asset Purchase Agreement between Novell and SCO dated 19 September 1995.

Late last month, Novell said in a letter to SCO that it retained the copyright to Unix. But SCO disagreed, citing Amendment No.2 to the Asset Purchase Agreement dated 16 October 1996.

Chris Sontag (pictured), senior vice president and general manager, SCOsource intellectual property division, said: "This amendment simply confirms SCO's long-stated position that it owns all copyrights associated with the Unix and UnixWare businesses.

"SCO is the owner of the Unix operating system, as well as all of the Unix contracts, claims and copyrights necessary to conduct that business.

"Because others have called into question SCO's ownership of the Unix and UnixWare copyrights, we are satisfied that we have now proven without a doubt that SCO owns those copyrights."

The company said that the amendment was signed by Steven Sabbath, vice president, law and corporate affairs at SCO, and James R Tolonen, executive vice president and chief financial officer at Novell.

Novell acknowledged that the document appeared to transfer some Unix copyright to SCO.

In a statement Novell said: "Amendment No. 2 appears to bear a valid Novell signature and the language, though convoluted, seems to support SCO's claim that ownership of some copyrights for Unix did transfer to SCO."

But it added: "The amendment does not address ownership of patents, however, which clearly remain with Novell."

Novell claimed that the amendment is not present in its files regarding the SCO transaction, and added: "Given that SCO released the amendment only today suggests that SCO, too, only recently became aware of it."

Novell reiterated its call on SCO to address the more fundamental issue which Novell raised in its 28 May letter. It describes this as "SCO's still unsubstantiated claims against Linux".

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