SCO Group ( SCOX) fired another salvo in its battle for legal control of the open-source Linux operating system Tuesday, suing Novell ( NOVL) over its claim to the Unix source code. SCO's suit in a state court in Utah claims Novell's copyright registrations for Unix don't hold water and that its actions have irreparably harmed SCO's business. The action is part of a larger legal strategy in which the Lindon, Utah, company is trying to gain control of Linux by proving it legally controls part of its core embodied in Unix. The company's shares have become a flyer on the litigation, which includes an ongoing suit against IBM ( IBM). They took a hit about a week ago when SCO lost a motion that would have forced IBM to turn over the code, but were up 75 cents, or 4.8%, to $16.20 Tuesday -- well over 10 times their level at the start of 2003. In its latest legal entanglement, SCO is charging that Novell has improperly filed copyright registrations in the U.S. Copyright office for Unix technology covered by SCO's copyrights. Novell's false and misleading representations that it owns Unix copyrights have caused SCO irreparable harm to its copyrights, its business and its reputation, SCO charges in a slander suit. SCO is seeking an injunction as well as damages. A Novell spokesperson was not immediately reachable for comment.