Researchers from Princeton University simulated an attack on a power network serving a population the size of California. The simulation found that a 1% surge in demand created by hacked smart appliances like air conditioners and water heaters could cause disruption to the network. This kind of attack is structured differently from many other grid attack and defense scenarios where hackers attack various central controls, and thus poses a unique set of security challenges.
Source: Hacked Appliances Could Shut Down the Power Grid, Researchers Say – Nextgov