SCO's contract dispute with IBM has been accompanied by a smear campaign against the whole GNU/Linux system. But SCO made an obvious mistake when it erroneously quoted me as saying that “Linux is a copy of Unix.” Many readers immediately smelled a rat—not only because I did not say that, and not only because the person who said it was talking about published ideas (which are uncopyrightable) rather than code, but because they know I would never compare Linux with Unix.
Unix is a complete operating system, but Linux is just part of one. SCO is using the popular confusion between Linux and the GNU/Linux system to magnify the fear that it can spread. GNU/Linux is the GNU operating system running with Linux as the kernel. The kernel is the part of the system that allocates the machine's resources to the other programs you run. That part is Linux.