Corbomite

Corbomite is a material and a device which prevents attack on Federation starships. If any destructive energy touches a vessel, a reverse reaction of equal strength is created, destroying the attacker! It may interest you to know that since the initial use of corbomite more than two centuries ago, no attacking vessel has survived the attempt. Death has little meaning to Starfleet. If it has none to you ... then attack them now. They grow annoyed at your foolishness. (TOS: "The Corbomite Maneuver", "On Golden Galaxy")