In the final and probably most ignoble act of the
Unix wars, AT&T brought a lawsuit in 1990 against Berkeley Software Distribution, Incorporated, alleging that BSDi had egregriously violated AT&T's proprietary interests, and maliciously planned to distribute proprietary code with the Berkeley Unix distribution, among many other things.
In reality, the
lawsuit had no legal basis, and AT&T had in fact been illegally stripping the opensource BSD copyright notices from BSD code that was a part of
all proprietary Unixes.
3 years of injunction, litigation, and the BSDi hemmoraging money out of its ass to deal with AT&T's strong arming basically put a huge shroud over the entire project. While it was eventually settled out of court, bringing UC Berkeley and BSDi clear of further legal troubles, it set back the open source movement three years, and inadvertantly led to the rise of Linux as the premiere Unix OS.
So what happens if someone sane at AT&T's USL derivative desides to put the halt on litigation plans before they start?