Hi,
That might have been true years ago, but today isnt it possible that they could interfere with the very infrastructure of a nation and cause a large amount of collateral damage?
For example, if a nuclear power plant or worse yet multiple plants could be infiltrated sufficiently think of what might happen.
The best example though i think is if the power grid went down in the whole country lots of people would die for various reasons.
Im sure there are safeguards in place for good reasons but there are often security breaches that are exploited before they are known to be a problem.
http://cybersquirrel1.com/
Nuclear power plants, power plants in general and grid are not interconnected to the point of a national shutdown being possible due to any type of Cyber-attack thank goodness and parts of the power grid (in the Texas area) are almost independent from the rest of the grid. It would take a massive real 'attack' of destroy the manual and offline backup systems that controls the entire power grid with legacy systems like hydro from the middle of the last century still being used.