SCO first filed this clue-challenged lawsuit in March 2003. SCO claimed Linux was contaminated with code IBM stole from UNIX and that it was impossible to remove the infringement. Therefore, said SCO, all Linux users owe SCO a license fee of $1399 per cpu — but since SCO are such great guys, for a limited time, you can pay only $699 per CPU for your dirty infringing copy of Linux.
Of course, Novell claimed and later proved in court that SCO doesn't even own the copyrights on UNIX that it is suing over.
IBM claims there is no infringing code in Linux. SCO never provided evidence of the massive infringement it claimed existed. The source ordered SCO three times to produce its evidence, twice extending the deadline, until it set a FINAL deadline of Dec 22, 2005 — which came and went — with SCO producing nothing but a lot of hand waving. Meantime, SCO filed for bankruptcy protection in September 2007 because it was being beaten up in court so badly with the court going against SCO.