Unknown individuals have breached the computer systems of three defense contractors that built Israels missile defense mechanism, Iron Dome. The incidents occurred in 2011 an 2012, but they have not been revealed until now.The hackers managed to steal large amounts of documents relating to the technology used for building the missile shield, which are of highly sensitive nature.Security blogger Brian Krebs learned from threat intelligence firm Cyber Engineering Services Inc. (CyberESI) …