The letters, dated Dec. 19, claim that the ABIs that allow customers to run Unix applications over Linux are owned by SCO and are being used without the company's permission. In the letter, SCO cites more than 65 examples of improper use of ABIs and header files in current Linux distributions.
The move comes as Novell works to intercept SCO's copyright claim by registering for copyrights on several versions of Unix System V with the U.S. Copyright Office over the past quarter.
Meanwhile, Linux Torvalds, creator of the Linux kernel, characterized SCO's latest intellectual property (IP) claim as technically hollow and baseless.
Nevertheless, in SCO's letter, and in a conference call held Monday to detail its latest IP claim, SCO insisted that use of its IP by Linux customers in a commercial setting violates company rights according to U.S. Copyright Law and the Digital Millennium Copyright Act (DMCA).