A mailbomb (or mail bomb), also called parcel bomb, letter bomb or post bomb, is an explosive device sent via the postal service, and designed with the intention to injure or kill the recipient when opened. They have been used in indiscriminate terrorist attacks such as those of the Unabomber. Some countries have agencies whose duties include the interdiction of mail bombs and the investigation of mail bombings .The mail bomb may have been in use for nearly as long as the common postal service has been in existence, as far back as 1764 (see Examples).