have we had any "cyber-terrorist" attacks in the U.S.?

I can think of two terrorist attacks on U.S. soil without too much difficulty: the World Trade Center and Oklahoma City. In both cases, computers and "internet" loosely defined played a minor organizational role. McVeigh used AOL, and the Trade Center bombers had some plans on a floppy disk. Have we had any instance of "cyber terrorism" -- you know, the kind of awful scenario which most people reading this could cook up without too much difficulty. or is the question not well formed since if it was a successful attack, we wouldn't know? -David