SCO has asked the court in its case against IBM to force Big Blue to hand over yet more code in the hope of finding lines that infringe what the company claims is its copyright.

After reviewing the Unix source code provided by IBM - something that delayed the trial because of the sheer size and amount of it - SCO appears to be having trouble find the code that it claims IBM wrongly contributed to the Linux open-source OS.

As such, it has asked the court to order IBM to produce more materials documenting the development of its AIX and Dynix operating systems, and argues that the files that IBM has produced to date are "incomplete".

In March, the court in Utah ordered IBM to provide SCO with source code to the two operating systems. It claimed in a filing last week that "the files previously produced by IBM pursuant to this Court's March order show that IBM improperly contributed code to Linux."

There were precious few details about the nature of these "improper" contributions, however, and SCO spokesman Blake Stowell has declined to say where, specifically, they are. IBM's most recent response has been blunt - asking the judge to throw the whole case out because SCO hadn't produced a thread of evidence.

SCO has admitted as much in its filings, saying "these efforts have not, however, yielded much of the information required for SCO to further respond to IBM's discovery demands". However, it claims that IBM is to blame. "SCO has attempted to follow IBM's scattered path through the winding history of countless alterations, derivations, and revisions, but the task is nearly impossible without a map, a map so easily accessible to IBM," it has stated. The solution? More of IBM's source code and developer contributions.

Even without flogging that horse to death, SCO is in dispute with Novell over whether it even owns the copyright to the code that it claims is infringed. And this week, it was forced to strike a deal with its main financial backer Baystar that would allow it to continue the legal battle after Baystar said it wanted out of the deal.

SCO's latest filings raise questions about how much evidence SCO actually has about any IBM wrongdoing with respect to Linux, given that SCO already has access to the open-source Linux source code, said Jeff Norman, an intellectual property partner with Kirkland & Ellis.

"We're talking about open source code. The code is out there," he said. "For them to say that they can't respond to IBM's request to identify specific items of code they are infringing, I just don't understand that. I don't think the judge is going to understand that. Either they know that there's code that's infringing or they're just fishing," he said.