A letter was sent to members of SCO's developer community indicating that they were suspending immediately their Linux efforts and were likely to go after the end users for copyright infringement.

The letter asserts (without any proof other than citing some people who had access to the original AT&T code as well as Linux) that Linux is an illegal derivative work of Unix.

IBM has already been sued by SCO, but so far companies that are derived from the BSD source code base have been spared threats. (Apple's OS X is based on FreeBSD, a BSD derivative).