E-4B is up callsign ORDER66
http://starwars.wikia.com/wiki/Order_66
Order 66, also known as Clone Protocol 66, was a top secret order identifying all Jedi as traitors to the Galactic Republic and, therefore, subject to summary execution by the Grand Army of the Republic. The order was programmed into the Grand Army clone troopers through the control chips implanted in their brains, making it impossible for the clones to disobey the command to turn against their Jedi Generals. The Kaminoan scientists who designed the clone troopers believed it was only to be used as a contingency protocol against renegade Jedi. In secret, Order 66 was the means by which the Sith intended to bring about the fall of the Jedi Order.