In his years-long career developing software for power grids, Stan McHann had never before heard the ominous noise that rang out last Wednesday. Standing in the middle of a utility command center, he flinched as a cyberattack tripped the breakers in all seven of the grid's low voltage substations, plunging the system into darkness. "I heard all the substations trip off and it was just like bam bam bam bam bam bam bam bam," McHann says. "The power’s out.

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