I freely admit to having a hard time following this one:

This high-technology soap opera is complex, but here is a simplified version of events so far: SCO, which bought the licensing rights to the Unix operating system and its source code in 1995, sued I.B.M. in March, contending that it breached its contract with SCO by shoveling Unix code into Linux, an operating system that is closely related to Unix. Linux is the leading example of open-source software development, where the code is distributed free and is then improved and debugged by a loose-knit network of far-flung programmers. I.B.M. has been the foremost champion of Linux among big companies.

A legal spat between two companies is a parochial matter, but SCO broadened its campaign last month. It sent warning letters to 1,500 large corporations that said, "We believe that Linux is, in material part, an unauthorized derivative of Unix."

....As the SCO story moves ahead, the most important question is: do Linux customers have a real cause for concern? The best answer, according to lawyers who have looked at the documents made public to date, is that as a legal matter it may be debatable, but as a practical matter almost certainly not.[NT Times]