The SCO Group has followed through on a threat it made in March and ordered IBM to stop using, selling and distributing its AIX operating system, which SCO claims is an "unauthorised derivative" of SCO's protected System V Unix code.
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SCO said it had "terminated IBM's right to use or distribute any software product that is a modification of or based on Unix System V source code".
SCO said it was taking the action under the "right of termination granted under the original 1985 Unix software and sublicensing agreements between IBM and AT&T," (which previously owned Unix before SCO obtained the software rights).
In March, SCO sued IBM for $1bn (£600m), alleging that IBM had misappropriated SCO Unix trade secrets by putting some of the code into Linux. SCO gave IBM 100 days notice, as required under the agreement, saying it would terminate IBM's AIX license if the company did not correct actions that violated the agreement.
SCO said IBM had failed to comply, thus triggering today's termination.
Trink Guarino, a spokeswoman for IBM's systems group, said there was nothing new in the latest salvo from SCO.
"SCO continues to make these claims," Guarino said. "As we have claimed all along, our licence is irrevocable. It is perpetual and it cannot be terminated" based on IBM's interpretation of its licence, he added.
SCO also said today it is filing an amendment to its complaint against IBM seeking a "permanent injunction" that would require IBM "to cease and desist all use and distribution of AIX and to destroy or return all copies of UNIX System V source code."
It is seeking monetary damages. The amended complaint, filed in the United States District Court of Utah, where SCO's court case against IBM was originally filed, seeks all money IBM earns from AIX after the expiry of the 100-day deadline.
Darl McBride, SCO's chief executive, said that his company is pursuing legal action to protect its intellectual property.
"IBM has chosen to continue the actions that violate our source code and distribution agreements," McBride said.
"Over the past several months, SCO has taken all of the steps outlined in the Unix licensing agreements to protect its rights. Today, SCO is requesting that the court enforce its rights with a permanent injunction. IBM no longer has the authority to sell or distribute AIX and customers no longer have the right to use AIX software."
Mark J Heise, an attorney who represents SCO in the case, said that the agreement between SCO and IBM "includes clear provisions that deal with the protection of source code, derivative works and methods".
By "contributing AIX source code to Linux and using Unix methods to accelerate and improve Linux as a free operating system, with the resulting destruction of Unix, IBM has clearly demonstrated its misuse of Unix source code and has violated the terms of its contract with SCO," Heise said.
"SCO has the right to terminate IBM's right to use and distribute AIX. Today, AIX is an unauthorized derivative of the UNIX System V operating system source code and its users are, as of this date, using AIX without a valid basis to do so."
The centre of SCO's position is its claim that it owns the Unix operating system, along with all the contracts, claims and copyrights associated with Unix. The company also alleges that portions of its System V code are found in Linux, as well as portions of resulting derivative code.
Last month, SCO warned all commercial Linux users that they could be using its code illegally and recommended that commercial users seek legal advice to help them to decide what to do about their use of Linux.
Novell called for SCO to "put up or shut up" in a letter from its chief executive Jack Messman.
He challenged SCO's assertion that it owns the copyrights and patents to Unix System V.
Novell, which had previously acquired the Unix systems business of AT&T Corp, broke up and sold its Unix properties in 1994 and 1995. One of those deals was with the former Santa Cruz Operation, which was bought by Caldera International and later became The SCO Group.
Todd R Weiss writes for Computerworld