The attack indeed came, a mere two and a half hours after we lowered our defenses. It was aimed at the plant's central system controls by means of a massive logic bomb, or as is commonly known because of its vast disruptive properties, an "I-bomb." We allowed the attacker to hack in, unimpeded.
The nature of the attack suggested that the hacker logged on to the key control systems by means of a brute-force password search, most likely. Then, once online, using the identity of a plant staff member, the hacker was limited only by the usual access controls to which employees are subjected. We let him proceed until a full trace was achieved...
Delay in taking defensive steps before shutting down the attack allowed partial detonation of the I-bomb - but we did at least avoid the massive cascading effects that would have accompanied a "clean" I-blast. The net result was that the reactor went near-critical, and, because of very strong onshore winds, there was a release of lightly radiated steam over an area populated by nearly 1 million people.