One of the most mysterious arts of feudal Japan was ninjutsu, Japan’s early day espionage system. Cloaked in secrecy, the original ninjitsu practitioners were the terrorists of their era. They were families of spies and assassins hired by Japanese warlords to infiltrate and terrorize enemies. Today, ninjutsu is practiced in a far more harmless fashion, minus the deadly overtones that characterized the original ninja warriors.