During the Dan Coates interview with Andrea Mitchell he said he is most worried about cyberspace attacks and listed a few examples. Are you?

There are all kinds of ways we could be crippled. Taking down power grids for instance. I don't know how difficult or how easy it would be to do but it worries me. If the internet goes down and stays down for days what would be affected? Would the damage be permanent or fixable? If a power grid does down how do we operate without electricity or power? I wonder if "the enemy" is currently working on it.