Spreading terror.

"Terrorism" is, admittedly, a very ill defined term. Academics have been arguing for decades about whether or not State actions against their own people can be labelled "terrorism" or not. Given that, I won't quote a dictionary or textbook definition, but rather say that I see them contributing as a part of a larger system that seems to meet some definitions of "terrorist", at least if you believe in the existence of "state terrorism".

It seems to me that their intent to be as clandestine as possible makes them distinctly non-terroristic.

Yeah, I'll admit that's an arguable point. I haven't even made up my own mind on the "intent" aspect.

All told, labeling them a "criminal" organization would probably be better, but I think it would be wrong to overlook the role they play in allowing the US government to use fear as a tool of control.