While it's more general malfunction than aggressive A.I. out for revenge, a computer-controlled anti-aircraft gun went haywire in South Africa, killed many soldiers nearby. (The one picture above is the same model, but not the same one.)
The anti-aircraft weapon, an Oerlikon GDF-005, is designed to use passive and active radar, as well as laser range finders, to lock on to "high-speed, low-flying aircraft, helicopters, unmanned aerial vehicles (UAV) and cruise missiles." In "automatic mode," the weapon feeds targeting data from the fire control unit straight to the pair of 35mm guns, and reloads on its own when its emptied its magazine.
Robot Cannon Kills 9, Wounds 14 [Danger Room]