What did the Iranians fire back with? A series of massive, on-going and ineffective DDoS attacks on American banks. This is a disproportionate response but not in the way military experts usually mean that phrase. It’s the equivalent of someone stealing your car and you throwing an ever-increasing number of eggs at his house in response.
It’s fascinating that Iran continues to do nothing more despite the fact that U.S. critical infrastructure currently has the defensive posture of a dog waiting for a belly rub. Keep that in mind the next time you hear that a "cyber Pearl Harbor" is imminent."