Novell has claimed it and not SCO holds the copyrights to Unix, and has blasted SCO's "intentionally vague" intellectual property claims against Linux vendors and users.

Launching a stinging attack on SCO, the Utah-based vendor demanded that the firm should provide more details of its allegations against Linux or take them back.

In a biting letter sent to Darl McBride, chief executive and president of SCO, Novell's chief executive and chairman Jack Messman (pictured) ripped into SCO's claims to own Unix, and said SCO had requested that Novell transfer the copyrights during the past months.

Messman called on SCO to provide details of its claim that its intellectual property had been added to Linux without its consent. He added that, contrary to SCO's claims, Novell still owns patents to Unix System V.

SCO's allegation that Unix System V code had been added into into Linux without its authorisation left critical questions unanswered, Messman said.

These questions included what specific code was copied from Unix System V; where can the code be found in Linux; who copied this code and why does the alleged copying infringe SCO's intellectual property.

"SCO claims it has specific evidence supporting its allegation against the Linux community. It is time to substantiate that claim, or recant the sweeping and unsupported allegation made in your letter," said Messman.

"Absent such action, it will be apparent to all that SCO's true intent is to sow fear, uncertainty, and doubt about Linux in order to extort payments from Linux distributors and users.

"SCO is not the owner of the Unix copyrights. Not only would a quick check of US Copyright Office records reveal this fact, but a review of the asset transfer agreement between Novell and SCO confirms it.

"To Novell's knowledge, the 1995 agreement governing SCO's purchase of Unix from Novell does not convey to SCO the associated copyrights.

"We believe it unlikely that SCO can demonstrate that it has any ownership interest whatsoever in those copyrights. Apparently, you share this view, since over the last few months you have repeatedly asked Novell to transfer the copyrights to SCO, requests that Novell has rejected.

"Finally, we find it telling that SCO failed to assert a claim for copyright or patent infringement against IBM."

Messman warned that SCO's actions are disrupting business at a critical time for Linux. "If carried forward, [SCO's actions] will lead to the loss of sales and jobs, delayed projects, cancelled financing, and a Balkanised Linux community.

"Further, we demand that SCO retract its false and unsupported assertions of ownership in Unix patents and copyrights or provide us with conclusive information regarding SCO's ownership claims."

In response, SCO has issued a statement saying that it owns the "contract rights" to the Unix operating system.

"SCO has the contractual right to prevent improper donations of Unix code, methods or concepts into Linux by any Unix vendor," SCO's statement said.

"Copyrights and patents are protection against strangers. Contracts are what you use against parties you have relationships with.

"From a legal standpoint, contracts end up being far stronger than anything you could do with copyrights.

"SCO's lawsuit against IBM does not involve patents or copyrights. SCO's complaint specifically alleges breach of contract, and SCO intends to protect and enforce all of the contracts that the company has with more than 6,000 licensees."