How vulnerable is our power grid in reality

coreboarder writes: Recently it was divulged that the Brazilian power infrastructure was compromised by hackers. Then it was announced that it was apparently faulty equipment . A downplay to the global public or an honest clarification? Either way it begs the question, how vulnerable are we really? With winter and all its icy glory hurtling towards those of us in the northern hemisphere, how open are we to everything from terrorist threats to simple "pay me or else" schemes?