The suits against DaimlerChrysler and Autozone were the first against corporate users of the Linux system, but just the latest twist in a legal battle over UNIX and Linux "open source" software created by Linus Torvalds as an alternative to Microsoft Windows and other operating systems.

Utah-based SCO said it was suing Autozone for "its alleged violations of SCO's UNIX copyrights through its use of Linux," adding that the company used "versions of the Linux operating system that contain code, structure, sequence and/or organization from SCO's proprietary UNIX System V code in violation of SCO's copyrights."

SCO said it was also seeking an injunction and damages from DaimlerChrysler in a separate action being filed in a Michigan state court.

"Today, we are moving to enforce the contract points agreed to by our end users," said Darl McBride, SCO's chief executive, on a conference call outlining the suit against DaimlerChrysler.

"We are aggressively moving forward to confirm our rights."

The suits are the latest chapters in SCO's ongoing fight to rein in what it believes is its right to revenue from the open-source Linux operating system. Linux is based on elements of Unix, and SCO holds the rights to some of the copyrights behind the operating system used in many enterprise computer servers.

In November, the company said it would sue Linux users who didn't sign intellectual-property agreements regarding their use of Unix. That move set off a flurry of lawsuits, including a five billion dollar claim SCO launched against IBM, charging Big Blue with improperly using Unix technology in its version of Linux.

Red Hat, one of the best-known Linux companies, has since sued SCO on the grounds that using Linux doesn't violate any SCO copyrights.

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