The process of evaluating the security of a system or network by simulating an attack on it. Sometimes called "ethical hacking" or white hat hacking. The phrase started to appear in U.S. military circles in the mid 1960s as time sharing computers became more necessary for daily operations. Computer security experts from Rand Corporation began describing computer compromises as “penetrations.” By the early 1970s, government leaders formed tiger teams of penetration testers to probe for weaknesses in various government systems.