I regularly say that, on the Internet, attack is easier than defense. There are a bunch of reasons for this, but primarily it’s 1) the complexity of modern networked computer systems and 2) the attacker’s ability to choose the time and method of the attack versus the defender’s necessity to secure against every type of attack. This is true, but how this translates to military cyber-operations is less straightforward. Contrary to popular belief, government cyberattacks are not bolts out of the blue, and the attack/defense balance is more…well…balanced.
Rebecca Slayton has a good article in International Security that tries to make sense of this: “What is the Cyber Offense-Defense Balance? Conceptions, Causes, and Assessment.” In it, she points out that launching a cyberattack is more than finding and exploiting a vulnerability, and it is those other things that help balance the offensive advantage.