Keep in mind that the electric grid is not a single system. It is essentially 3 separate interconnected "groups" of systems whereby each utility entity operates its own system using its own operating control. In addition, the system can be operated manually, right down to opening and closing circuit breakers.
That said, it's not perfect, and under the right circumstances, a virus in one entity's system can bring about cascading outages and in the worst case scenario, can result in a total shutdown of one of the 3 regional areas.
Now, the electric power industry has built up significant firewalls and practices to protect their electronic infrastructure so they're not easy to get to. But things can happen. We in the power industry are pretty vigilant, and have ways of operating sans the central control system.
Makes me feel MUCH better to hear that. Sincerely thank you.