Well, I do agree that samurai was misinformed when he said "ninjas did not live by a code." They very much did so. Everything was duty to them. The first ninjas, from my research,(and believe me, I have researched and apply the lifestyle of the ninja in every way of my life, from the minute I wake up til the moment I sleep. I even looked up ninjan food recipes!) were actually priests who developed the skill of stealth to hide from men who were after them, due to the fact that priests have always held power througout history. Eventually the secrets of the priests made it into public hands, and their stealth skills were combined with fighting syles to create ninjutsu. Ninjutsu is literally "the art of being invisible." Ninjas were not really the "enemy" of samurai, like many movies depict. In fact, ninjas often worked for high-ranking shoguns and daimyos(samurai warlords.) That is some basic info. Here are some more good sites for ninja-ish stuff. http://www.iganinja.jp/english/menu.html http://www.ashidakim.com/
There you go, and enjoy your study of the shadow warriors!