One thing I’ve heard a lot of people talk about recently is the need to develop good theories of cyberdeterrence. It’s making the think tank rounds and what not. But the basic assumptions that cyberdeterrence is needed, or doesn’t exist, etc. aren’t obvious to me.
Let’s take the PRC as a case in point. Based on a lot of pretty strong and publicly discussed circumstantial evidence, it seems reasonable to assume that the PRC is constantly attacking US computer networks, conducting industrial and governmental espionage and laying the groundwork for damaging cyberattacks in the event of hostilities. Lots of people are spending a lot of time, effort, and money to try to mitigate the attacks that are already occurring, and especially the ones that have not yet occurred. And all of these people, myself included, are convinced that we are and will continue to be behind the curve. Since it seems like so many people like to arrogate the terminology of Cold War standoff, I will follow suit and say that the best we can (or should try to) do is “containment”. 
This is a fundamental issue in security—not just information security. Professionals mitigate risk and concern themselves with threats, not vulnerabilities. Attacks will inevitably happen. Some will be more successful than others. The point is to work to avoid the most serious, probable, and predictable ones, while trying to detect all attacks and mitigate their effects—that is, to contain attacks. Addressing threats dictates the nature of security approaches, deployments and technologies. And while it is fundamentally defensive in nature, it acts as a deterrent in its own right. Fewer businesses are physically robbed because there are video cameras and silent alarms when it makes sense to have them, and everybody knows it. Fewer individuals attempt serious attacks on DoD because they know people are watching, and getting caught means they’ll (get extradited and) go to prison. And so on.
Containment in the sort of sense indicated above (or in the original sense intended by Kennan and [mis]appropriated by the wider defense intellectual community) is a form of deterrence. It also relies on more overt, less subtle forms of deterrence (read: the threat of overwhelming force, or containment à la Nitze) in order to be effective. But we have that anyway in our military.
As I’ve suggested elsewhere, the PRC may very well be using cyberattacks to deter conventional attacks:
the PRC is already deterring the US by its apparent low-level attacks. These attacks demonstrate a capability of someone in no uncertain terms and in fact may be a cornerstone of the PLA’s overall deterrence strategy. In short, if the PLA convinces US leadership that it can (at least) throw a monkey wrench in US deployments, suddenly the PRC has more leverage over Taiwan, where the PLA would need to mount a quick amphibious operation. And because it’s possible to view the Chinese Communist Party’s claim to legitimacy as deriving first of all from its vow to reunite China (i.e., retake the “renegade province” of Taiwan) one day, there is a clear path from the PLA cyber strategy to the foundations of Chinese politics…The PLA has concluded that cyber attacks focusing on C2 and logistics would buy it time, and presumably enough time (in its calculations) to achieve its strategic aims during a conflict. This strategy requires laying a foundation, and thus the PRC is presumably penetrating networks: not just for government and industrial espionage, but also to make its central war plan credible.
The US, on the other hand, can clearly deter serious cyberattacks through its conventional military, not least because serious cyberattacks will be paired with kinetic attacks, and attribution won’t be a problem. I’ve talked about this elsewhere and won’t belabor it here.
But the idea that we should more actively deter cyberattacks using cyber methods is out there. It is based on unrealistic technological assumptions, but more importantly it’s fundamentally wrong. It doesn’t make sense from the point of view of political or military objectives. The US wouldn’t gain anything from a cyberdeterrent: it treats cyber as a strategic capability, and wouldn’t use it just to deter the sorts of cyberattacks that it faces now. And the PRC wouldn’t use any more of its presumptive cyber capability than the bare minimum required for the PLA’s purposes—and note that the likely PLA strategy would also require a powerful reserve (but not in the sense of “second-strike”) capability.
If cyberdeterrence is supposed to mean deterring cyberattacks using cyber methods, we’re better off without it. If cyberdeterrence means just about anything else, we’ve either already got it or have already decided against it.
 Containment, as originally intended by Kennan, was not a strategy of constant military opposition. Kennan did not believe that the USSR was a grave military threat to the US (or to Western Europe), and went to some lengths to clarify this point in his later years, but he very much believed that the USSR was an entity that needed to be opposed. Its influence needed to be contained so that it could not gain ground in Europe through political and economic means: these were the Soviets’ preferred avenues for expansion.
Although the USSR possessed a tremendously powerful military machine at the end of World War II, the US held a clear strategic advantage at the time of the long telegram, and until the Soviets had more than a handful of atomic bombs, they did not have the minimum means of reprisal to counter a US attack. It was only decades later that the USSR presented any direct military threat to the United States homeland. It’s important to remember that not only was NATO always intended to demonstrate American commitment to Europe through placing troops as hostages to a Soviet strike, but that the demonstration was as much (if not more) for the benefit of the Europeans as for the Soviets.
In short, the strategy of containment was not originally intended as a justification for a colossal military counterweight to the USSR, but as justification for a clear commitment to providing a viable political and economic alternative—backed up by force, but not based on the threat of its use. Instead the threat became the message.