The SCO Group's struggle to keep its Linux-related lawsuits against IBM and Novell viable on Monday faced increasingly dismal prospects.

SCO attorneys awoke Monday to a new legal effort by Novell that could, if successful, fatally undermine the foundation for both its $5 billion contract and copyright suit against IBM, and its "slander of title" case against Novell.

SCO, the Lindon-based software company, has spent tens of millions of dollars on the cases in more than 3 1/2 years of litigation. It contends IBM illegally leaked SCO-owned Unix code into the freely distributed Linux operating system; and it is suing Novell for claiming it, not SCO, owns Unix.

Specifically, Novell asks federal Judge Dale Kimball to declare that Novell had the right to issue a waiver to IBM for Unix use when SCO refused Novell's demands to do so three years ago. If that waiver is upheld, then SCO's claims could be argued to be based on nonexistent rights.

SCO has insisted that for the more than $100 million it spent on Unix in 1995, it obtained all rights to the code and its use. Novell counters that the purchase limited what assets SCO acquired while safeguarding "certain Unix rights" for Novell.

The motion was filed late Friday, the day after Kimball upheld Magistrate Judge Brooke Wells' June decision striking two-thirds of SCO's case against IBM.

SCO attorney Stuart Singer acknowledged Novell's latest motion "obviously is directed at the heart of the case. [But] we believe it is mistaken, and we will vigorously oppose it."

SCO's share prices continued to plunge to levels not seen since before it first filed suit against IBM, in March 2003 -- and raised the specter of delisting by the Nasdaq exchange, which requires members shares to trade at $1 or more.

SCO shares closed Monday at $1.11, down 11 cents and 9 percent from last Friday's trading. The company's stock has been in freefall since Kimball's ruling, dropping from $2.40 per share. SCO stock had traded above $4.50 before Wells' earlier decision in June.