On March 7, 2003, a struggling company called The SCO Group filed a lawsuit against IBM, claiming that the
success of Linux was the result of a theft of SCO’s technology. Two
decades later, it is easy to look back on that incident as a somewhat
humorous side-story in the development of Linux. At the time, though, it
shook our community to its foundations. It is hard to overestimate how
much the community we find ourselves in now was shaped by a ridiculous
lawsuit 20 years ago.

Source: LWN.net – [$] The SCO lawsuit, 20 years later