An internal investigation at SCO in 1999 reported that not a single line of code in the Linux kernel was found that violated SCO's copyright, according to an email datad 13 August 2002 which was obtained by legal website Groklaw. 

Bob Schwartz, an outside consultant, spent between four and six months comparing Linux with the so-called AT&T Unix code.

"SCO was sure that it was going to find evidence of copyright violations," a SCO employee wrote in an internal email. "At the end, we had found absolutely nothing: no evidence of any copyright infringement whatsoever."

In cases where there was an overlap between SCO's Unix code and Linux, both software suites obtained the code legitimately from some third party, the email stated.

The message was addressed to SCO senior vice president Reg Broughton who forwarded it to chief executive Darl McBride.

SCO made a statement in response to the posting: "This memo shows that Mr Davidson's email is referring to an investigation limited to literal copying, which is not the standard for copyright violations and which can be avoided by deliberate obfuscation, as the memo itself points out.

"Even more importantly, this memo shows that there are problems with Linux. It also notes that additional investigation is required to locate all the problems, which SCO has been continuing in discovery in the IBM and Autozone cases.

"Thus, even aside from the fact that SCO's central contract claims in the IBM litigation involve later Linux versions and different conduct, it would simply be inaccurate and misleading to use Mr Davidson's email to suggest that SCO's internal investigation revealed no problems."

SCO filed a lawsuit against IBM in 2003, demanding mor e than $1bn in damages for alleged copyright violations. SCO claims ownership of the so-called AT&T Unix source code and alleges that Linux developers copied parts of the code.

The case has been slowly proceeding through the courts, but SCO has not yet produced any proof of the copyright violations.

Although the email obtained by Groklaw pleads against SCO, it does not suggest that the company has no other evidence that incriminates Linux and IBM.  When contacted IBM declined to comment.