SCO claims IBM is distributing the Linux software containing its copyrighted Unix code. It claims companies such as Red Hat Inc. are building products using the same code. The company broadened its legal attack by suing AutoZone for using software that contains the code, and DaimlerChrysler for not certifying that Unix, which it obtained via license with SCO, has been used inappropriately.

DaimlerChrysler spokesman Han Tjan said he had no comment on SCO's suit. AutoZone Chief Executive Steve Odland declined to comment on the claims. IBM spokeswoman Trink Guarino said the suit is groundless and the company will contest it.

Linux, invented in 1991 by Torvalds as a student in Finland, found converts in part because it was a free, publicly shared operating system. Anyone can work on and modify the source code of Linux. By contrast, Microsoft licenses its Windows code only to select partners, which don't have permission to make changes.

McBride is getting the most heat from the thousands of volunteers who have worked on Linux over the past 13 years. They say SCO has no claim on the code.

"The real reason why people don't like SCO, and Darl McBride in particular, is that he is so dishonest," Torvalds, 34, said in an e-mail.

McBride has done battle before. He compares his fight with Linux supporters to the time when his family caught thieves stealing cattle from their ranch in Utah.

"We brought those guys to justice," he said. "It's very similar to what we are dealing with here."

As a young man, McBride participated in rodeo events and helped perform chores with his cowboy father, Pat. Together, they tamed wild horses. He graduated from Brigham Young University after serving as a missionary with The Church of Jesus Christ of Latter-day Saints in Japan.

In January, McBride's unlisted home telephone number was placed on Slashdot.org, a pro-Linux Internet site, which led to harassing phone calls on Super Bowl Sunday. Hackers also targeted the company's Web site with the Mydoom virus earlier this year, causing the company to shut down the site.

McBride said he sometimes carries a gun, declining to specify the type, and travels with armed guards. The gun is licensed, he said. Security officials have told him that convicted felons are behind the death threats, McBride said.

"When those are the types of people who are making threats on your life, you tend to take it more seriously," he said.