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Possible candidates could include HP-UX and IBM's AIX, both of which have huge installed user bases. McBride said Sun's Solaris Unix operating system was "the most clean" of patent infringement.
McBride defended his company's decision to mail out a letter to the world's largest businesses in May warning that Linux was an "unauthorised copy" of SCO's intellectual property. "We can show direct lines of our code showing up in Linux, which makes it pirated software," he said.
Commenting on the legal case against IBM, McBride said, "Unix System V code has been copied line by line into the Linux kernel." He said IBM had donated code in Unix System V, such as support for Numa hardware, to the open source community.
Last week, 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". As a result, IBM can no longer distribute its AIX operating system.
In a written statement, IBM said its Unix license is irrevocable, perpetual and fully paid up. "It cannot be terminated. IBM will defend itself vigorously. This matter will be resolved in the normal legal process." IBM reassured users that it would continue to ship, support and develop AIX.