IBM has returned fire at The SCO Group, which has been battling to assert claims that it has the right to collect license money from Unix users.

SCO is suing IBM for $2 billion ((£1.86 billion) claiming IBM to be breaking its Unix contract by allowing its code to be added to Linux. IBM's retort is to accuse SCO of violating the GPL (general public license) governing contributions to the Linux operating system, and that SCO has also infringed upon four IBM patents.

SCO's claims pertaining to Unix are affecting the entire Linux and Unix community, as the company hopes to build for itself the right to collect license money from some Unix and Linux users.

The company has one major supporter – Microsoft. That company is known to view Linux and Unix as threats to its operating system dominance, particularly in the corporate markets. Microsoft licensed SCO's Unix technology on May 19 in a move that many saw as legitimizing SCO's claims.

Big Blue's justice mission

In its countersuit, IBM alleges: "These counterclaims arise from SCO's efforts to wrongly assert proprietary rights over important, widely-used technology and to impede the use of that technology by the open-source community. SCO has misused, and is misusing, its purported rights to the Unix operating system developed initially by Bell Laboratories, then a research and development arm of AT&T, to threaten destruction of the competing operating systems known as AIX and Linux, and to extract windfall profits for its unjust enrichment," IBM said.

SCO filed a suit against IBM in March claiming that IBM has tried to undermine the Unix operating system, the rights to which SCO claims to own, with its Linux development efforts.

SCO has "falsely asserted" that it has the right to revoke IBM's Unix license, IBM's complaint said. SCO announced in June that it was terminating IBM's AIX license and would seek compensation from IBM's AIX business. AIX is a version of Unix developed by IBM.

IBM's "irrevocable rights"

Novell sold certain Unix System V rights that it had acquired from AT&T to Santa Cruz Operation in 1995, but it did not grant that company the right to revoke Unix licenses, IBM said. SCO, formerly known as Caldera, bought the Unix rights in question in 2001 when it acquired some assets of Santa Cruz Operation.

Those Unix rights did not include the right to revoke IBM's license, which is described as "perpetual and irrevocable" in the complaint, according to Novell and IBM. IBM attached letters from Novell to SCO from June of this year to support its claims in the complaint.

Linux users on SCO hit-list

In a move to boost its popularity among open source advocates, SCO announced this week that it will attempt to collect licensing fees from Linux users.

By attempting to claim licensing fees on Linux, SCO is in violation of the GPL, IBM said. It also said that SCO agreed not to seek such fees on any software distributed under the GPL when it distributed its own Linux products under that license using source code developed by IBM.

The patent-infringement charges center around four SCO products, UnixWare, Open Server, SCO Manager, and Reliant HA, IBM said. SCO infringed four separate IBM patents with those products, and should be enjoined from developing or selling those products, IBM claims.

The patents that are being infringed, according to IBM include: a patent called "Data Compression Method;" one called "Method of Navigating among Program Menus Using a Graphical Menu Tree;" one called "Self-Verifying Receipt and Acceptance System for Electronically Delivered Data Objects;" and "Method for Monitoring and Recovery of Subsystems in a Distributed/Clustered System."

Responding to IBM's claims, SCO said: "We view IBM's counterclaim filing today as an effort to distract attention from its flawed Linux business model.

"SCO reiterates its position that it intends to defend its intellectual property rights. SCO will remain on course to require customers to license infringing Linux implementations as a condition of further use. This is the best and clearest course for customers to minimize Linux problems."

SCO "outgunned"?

Ovum analyst Gary Barnett told Computing magazine: "When IBM fires a broadside it is a very carefully prepared action, which will be very carefully executed.

"IBM has more patents than anyone, and more money and more lawyers than SCO. SCO will be bled dry before it can make its case," he claimed.

Apple uses a variant of Unix in Mac OS X. This is based on a version called Berkeley Software Distribution, originally developed by AT&T, but not covered by SCO's license.

Despite that, Apple is also facing litigation from the Open Group, which wants Apple to put OS X through tests to ensure it meets OPen Group's standards for using the Unix brand.