Aircraft hijacking is the take-over of an aircraft, by a (usually) armed person or group. Unlike the hijacking of land vehicles, it is usually not perpetrated in order to rob the cargo. Rather, most aircraft hijackings are committed to use the passengers as hostages and to obtain transport to a location. In the September 11 Terrorist Attack, 2001, the use of hijacked planes as suicide missiles changed the way hijacking was perceived as a security threat.