Spies in Japan have been around for well over a few centuries. Ninjas, also known as shinobis were undercover spies or mercenaries, were known for their stealth and methods of deception, and are said to have risen during the time of feudal Japan. The main tasks which ninjas were assigned ranged from spying, sabotaging, infiltrating and last but not least, assassinating or even protecting high risk targets. They served even as personal bodyguards. Unlike the samurai, ninjas or shinobis were considered dishonorable and well beneath the strict set of codes of honor that reigned the samurai realm. Shinobi spies and mercenaries had already been observed to act covertly during as far back as the Sengoku period, in the 14th and 15th centuries. Some sources even claim the possibility that they even may have operated during the Heian or Kamakura periods, well into the 12th century.
According to some historical records, the ninjas, or shinobis, spelled either 忍者 or 忍び in Japanese were already involved in the Genpei War, a war in which the legendary Minamoto no Kuro Yoshitsune hired mercenaries to help him defend his palace during sieges. It is often said that during the era of Kenmu, Masashige Kusunoki, ninjutsu was already a rather cultivated art of war form. The War of Genpei is estimated to have gone on for at least 5 years, starting in 1180. Ninjutsu is believed to have been developed by indigenous peoples from the Japanese regions of Iga, Kouka and Shiga.
Ninjutsu was a sort of collection of survival methods for times of war in Japan during the feudal era. Ninjutsu practitioners made use of their martial art skills which included espionage, stealing strategic information, stealth and deceit. Ninjas also were highly skilled in the art of disguise, concealment, free running and even archery.