A berserker droid.

Berserker droid was the term given to any droid that ignored its programming and reacted violently to a threatening situation. This term was commonly used during the time of the Galactic Republic.

The level of violence among berserker droids varied from model to model, though in all cases, internal threat-avoidance routines were bypassed by the droid. Many times, this aberrent behavior was inititally overlooked or dismissed by the droid's owner, who simply had the droid's memory erased in an attempt to remove the "glitch". However, berserkers were unaffected by memory wipes—in fact, this action only added another layer of incoherence to the confused droid. Over time, these droids abandoned their programmed role and took up less lawful endeavors, until their programming simply imploded and they became killing machines.