The SCO Group has responded robustly to IBM's attempt to have a US district court dismiss some of SCO's main claims in its multi-billion dollar lawsuit.

SCO's case alleges that IBM broke its Unix contract by putting SCO's code into the open source Linux operating system.

According to IBM, the code in question is not taken from the core Unix System 5 code that is licensed from SCO, and so does not belong to SCO.

Big Blue's motion for summary judgment states: "Although SCO for months perpetuated the illusion that it had evidence that IBM took confidential source code from Unix System V and 'dumped' it into Linux, it has become clear that SCO has no such evidence."

IBM contends that the main claim against it now rests with SCO's "wrong" assertion that contributing IBM's own code from IBM's two Unix-based operating systems, AIX and Dynix, breached the contract.

But SCO has been quick to issue a statement, in which it claims that IBM, through its contributions of AIX into Linux, was in breach of this software agreement.

"SCO disagrees with IBM's interpretation of their contractual obligations regarding derivative works," the company's statement said.

"The SCO Group is the sole owner of the AT&T Unix System V software licensing agreements, including the software agreement that IBM entered into when they licensed Unix System V in order to create their derivative work known as AIX."

IBM has argued that, even if it had put Unix code into Linux, Novell had retained rights over Unix covering this when it passed Unix to SCO, and had waived them on behalf of SCO.

But SCO has contested Novell's claim to have retained the Unix copyright. Last week Novell moved to have SCO's case against it dismissed.

Blake Stowell, SCO's public relations director, told vnunet.com: "We will answer [Novell's] filing with a response filing in the very near future.

"It's worth noting that the judge in the case has already denied Novell's earlier request to have this case dismissed."

The hearing on IBM and SCO's counter-motions is likely to take place on 15 September.