code is derived: This is very important, because early Unix source code does not have any copyright claim. At that time, the law required explicit copyright claims, which effectively means the early Unix code is not protected by copyright law. Additionally, both Santa Cruz Operation and The SCO Group released the source code of early versions of Unix under a 4-clause BSD-like license, allowing its use in other open source products. SGI response On October 1, 2003, SGI responded to SCO's allegations in an open letter to the Linux community. In it, Rich Altmaier, vice president of software, claims that these small code fragments were inadvertently included in the Linux kernel: See also SCO-Linux controversies USL v. BSDi References External links SCO's evidence of copying between Linux and UnixWare SCO's Evidence: This Smoking Gun Fizzles Out Analysis of SCO's Las Vegas Slide Show SCO–Linux disputes Silicon Graphics