One of the first observers to see the evidence in the SCO Group Inc.'s intellectual-property claim against IBM and the Linux community says there are direct similarities between the Unix code that SCO claims control over and the Linux operating system.

"My impression is that [SCO's claim] is credible," says Laura DiDio, a Yankee Group analyst who was shown the evidence by SCO Group earlier this week. "It appears to be the same" code. But DiDio says the developing battle could hinge on legal fine points that are hard to sort out in the current atmosphere of claims, denials, and counterclaims.

Apparently the most telling evidence is that parts of the SCO code and Linux code include identical annotations made by developers when they wrote the programs, says DiDio, who compares such notes to the signature or fingerprint of a developer's work. "The fact that these appear to be transposed from Unix System V into Linux I find to be very damaging." DiDio says she was shown several instances where the source code and developer's comments in one operating system were the same as in the other operating system.

SCO Group has filed a $1 billion lawsuit against IBM over the matter, and it warned Linux users that they could be liable as well. In a letter sent March 6 by SCO Group CEO Darl McBride to IBM CEO Sam Palmisano summing up its claims, SCO charged that IBM has subjected SCO Group's "trade secrets to unrestricted disclosure, unauthorized transfer and disposition, unauthorized use, and has otherwise encouraged the Linux development community to do the same." SCO warned that it could revoke IBM's license for the AIX operating system on June 13 if IBM does not remedy the situation.

IBM shows no signs of conforming to SCO Group's demands. "IBM believes our license is irrevocable and perpetual," a spokeswoman says. "And we have the right to continue shipping AIX according to the terms of the contract."

DiDio says she's recommending that companies using AIX or Linux systems from IBM check the fine print in their contracts to see how well they're covered against potential claims from SCO Group. "Then I'd talk to IBM and say, 'How are you going to help me out?'"