SCO Group has claimed Linux users will still need to buy one of its licences even if they find and replace the code it claims was misappropriated from its Unix operating system and "dumped wholesale" into Linux.
Industry experts have previously said any contentious code in Linux could easily be replaced. But SCO plans to extract a licence fee for the time its code was being used within Linux, if it can prove such code has been misappropriated this way.
In July when SCO announced its licensing programme for users of Linux software containing the 2.4 kernel or above, Linux distributors SuSe and Red Hat said the infringing code could be replaced in weeks if not days if SCO was to go public with it, negating the need for users to buy a licence.
Then at the recent Linux World event another company unveiled a product it claimed would help Linux users "sniff out" the offending code on their servers.
However, Chris Sontag, senior vice-president and general manager of SCO's source division, said even if users were able to replace the infringing code - a feat he did not believe was possible - the company would pursue them for compensation claims through its licensing programme.
"For one thing [replacing the offending code] doesn't solve the past problems," he said.
Red Hat and SuSe are also "significantly underestimating the size of the problem", said Sontag. "The amount of Unix code in Linux could be greater than 25%."
He also pointed out that only SCO has the right to look at its Unix code and it has no intention of allowing others such as Red Hat to review it.
While it has been silent on the details of its complaint, SCO is now fleshing out its legal argument. Linux 2.4 and 2.5 kernels contain at least 1,549 files "misappropriated" from Unix, according to SCO.
Sontag said this code is in all of the Linux distributions based on the 2.4 kernel, including those from Red Hat and SuSe. He added that the 1,549 figure could rise as SCO continues its efforts to discover further examples of infringing code and files in Linux.
"That is just the number identified so far. It will probably end up being a lot higher," he said.
SCO president and chief executive officer Darl McBride claimed "the DNA of Linux comes from Unix" and if the offending code was to be taken out of Linux it would be equivalent to taking out the middle 30 floors from a 60-floor building.
SCO has maintained that wholesale misappropriation of Unix code from its proprietary Unix operating system by IBM and others had been critical to the growth in Linux uptake.
According to SCO the previous 2.2 kernel was "a hobbyist-level technology" with two-way multi-processor capability and "moderate" reliability.
In contrast Sontag said the 2.4 kernel offers an enterprise-level technology with 32-way multiprocessor capability in symmetrical multiprocessing configuration. This SMP functionality in Linux kernels 2.4 and 2.5 is by far the biggest area where SCO believes its Unix code has been misappropriated. SCO claims 1,185 files have found their way from its copyright Unix System V operating system into Linux.
As well as comparing code contained in the Linux 2.4 and 2.5 kernels with its own Unix code to try and identify examples of "literal" line-for-line copying.
Sontag said SCO is using pattern recognition software to find examples of "obfuscated" code where the original Unix code had been altered slightly "with intent" by IBM and others to try and hide its origins.
This was first published in August 2003