In computer programming, evil is that which leads unpredictably to deviant behaviour. It is invoked by the the actor that plays the wrong role, the conductor that embarks upon the wrong score, and by that member of the cherished public who pulls the fire alarm after the lights have gone down and the curtain has gone up. Evil is waiting at the threshold of every condition, the boundary of every array, between the lines of every automatically-generated expression, script, and compilation unit. It sleeps within compiler optimisations and winds its way by flaws in the protocol and holes in the implementation through the nodes of the network. Evil is that which is undefined, that which is poorly defined, and that definition which is ignored. It's the wrong time, the wrong place, the face that's lovely, but the wrong face.