The computer worm known as Stuxnet was discovered this past July and specifically targets computers that run critical infrastructure such as the electric power grid, water treatment and oil and gas pipelines.
Looks like we have a bit of a "super virus" on our hands here- a very sophisticated one at that. Man, if this thing were to get into power grid computers, we'd be sunk.
http://www.cnn.com/2010/TECH/web/11/17/stuxnet.virus/index.html?hpt=T2