How much at risk is the U.S.'s critical infrastructure?

itwbennett writes: There is growing evidence that intrusions into the power grid and other critical infrastructure by hostile foreign nation states is real and happening. But there's 'much less agreement over how much of a threat hackers are,' writes Taylor Armerding. 'On one side are those – some of them top government officials – who have warned that a cyber attack on the nation’s critical infrastructure could be catastrophic,' writes Armerding. While others, including C. Thomas, a strategist at Tenable Network Security, who got some attention when he argued in an op-ed in the Christian Science Monitor that the biggest threat to the U.S. power grid or other industrial control systems (ICS) is not a skilled hacker, but squirrels, are crying FUD. Who has it right? Agreement seems to coalesce around two points: 1) the cyber security of ICSs remains notoriously weak and 2) hostile hackers will improve their skills over time. So while we haven't reached 'catastrophe' yet, a properly motivated terrorist group could become a cyber threat.