Wouldn't a "microwave attack" lead to a massive burning sensation? I also think it's far more likely that it's some kind of surveillance technology (or even something less nefarious) with unintended side-effects rather than a legitimate "attack".
Unless the microwave oven is severely damaged, the shielding should prevent any "leakage" so it's probably just psychological. If you somehow manage to remove the door and still keep it running, though, things get fun.