Get the proof the court ordered and all SCO's credibility problems go away. Fail to do so, and SCO goes away.

SAN FRANCISCO, Dec. 22 - Novell Inc. has quietly registered for the copyrights on many versions of the Unix computer operating system that the SCO Group already says it owns, further muddying the water surrounding a dispute that has embroiled the Linux open source world for almost a year.

SCO, which has sued in an effort to capture hundreds of millions of dollars in licensing fees and damages from I.B.M. and other companies, said it owned the rights to the Unix operating system through a transfer from Novell dating back to 1995. SCO asserts that Linux, a variant of Unix that is distributed free and has been making significant gains in corporate computing, violates SCO's license and copyright.

SCO reacted on Monday to Novell's decision to register for the Unix copyrights by calling the move a backdoor act to claim code that is rightfully SCO's. "We see this as a fraudulent attempt by Novell to get something they don't have," said Darl C. McBride, president and chief executive of SCO. "It's fraudulent to now go and say they have these'' copyright registrations.

Mr. McBride contended that Novell was acting as a stalking horse for I.B.M., the biggest seller of Linux to corporations. "It's not just Novell,'' Mr. McBride said. "It's an attack by I.B.M."

An I.B.M. spokesman declined to comment, noting that the company is in litigation with SCO. SCO filed a breach of contract and trade secrets lawsuit against I.B.M. last March, accusing I.B.M. of illegally incorporating Unix code in Linux. In that suit, SCO is asking for $1 billion in damages. I.B.M. has denied the charges, saying that SCO has not shown that the Linux software violates any copyrights.

On Dec. 5, a Utah court told SCO that it had 30 days to demonstrate to the court exactly what parts of the Linux code I.B.M. is using that infringe on its rights.

Novell executives confirmed that the company filed for copyright registrations this fall, but declined to provide details. "Novell believes it owns the copyrights in Unix, and has applied for and received copyright registrations pertaining to Unix consistent with that position," Novell said in a statement. "SCO has been well aware that Novell continues to assert ownership of the Unix copyrights."