Shinobi is the name of a game by Sega, which was originally released on arcade machines in 1987, and later on home computers. Versions were released for the Nintendo NES, Sega Master System, Commodore 64, Amiga, Atari ST, Amstrad, ZX Spectrum and MS-Dos PC.
In the game, you are a Joe Musashi, a ninja, who works for the government as a secret agent. You have to rescue the children of the world's leaders, since they were kidnapped by the Ring Of Five, a terrorist organization led by five evil ninjas with strange super powers.
You can defeat your enemies by kicking them, throwing shurikens at them, or using the various weapons that you can pick up along the way.

Your quest takes you through five levels, each of which is split up into three or four stages. At the end of the level, you have to defeat the end-of-level boss. The five levels were Ken Oh, Black Turtle, Mandara, Lobster and Masked Ninja. After completing a level, there is a bonus stage, in which ninjas jump towards you and you have to kill them by throwing shurikens at them before they reach you. Defeat them all, and you'll get an extra life. If you fail, you just continue to the next round.

Because of its popularity, the game spawned many sequels and clones for the home computers. I never played Revenge Of Shinobi or The Cyber Shinobi, but I did enjoy Shadow Dancer on the arcade machine, but I never knew it was an official sequel of Shinobi until I did some research for this write-up. I always thought it was a clone.

As Moodster pointed out to me, the names in the game are obviously inspired by The Book Of Five Rings by Miyamoto Musashi.