The static nature of current computing systems has made them easy to attack and harder to defend. Adversaries have an asymmetric advantage in that they have the time to study a system, identify its vulnerabilities, and choose the time and place of attack to gain the maximum benefit. The idea of moving-target defense (MTD) is to impose the same asymmetric disadvantage on attackers by making systems dynamic and therefore harder to explore and predict. With a constantly changing system and its ever adapting attack surface, attackers will have to deal with a great deal of uncertainty just like defenders do today. The ultimate goal of MTD is to increase the attackers’ workload so as to level the cybersecurity playing field for both defenders and attackers - hopefully even tilting it in favor of the defender.