MAD
During the cold war, the doctrine of MAD (mutually assured destruction) led to the end of direct warfare between the major powers. The potential that any conventional conflict could slide into a nuclear war, where both the attacker and the defender were destroyed (a Nash equilibrium), was the deterrent. We may shortly see a reprise of this concept for warfare between states in an interdependent world, where disruption replaces destruction in a new MAD.
In a globally competitive marketplace, ongoing disruption of a single country's economic system can result in rapid declines in relative performance. Computer assaults can accomplish this result with a high level of deniability. The option for Estonia is clear, will it establish a similar capability alone (or in conjunction with other states to form an umbrella of protection) to make the new MAD a reality? The best approach for this is to develop an open source network of hackers/black marketeers that can match the Russians. That shouldn't be hard. It's also possible to easily scale the impact of the attacks such that the damage to the larger state is equal or greater than to the smaller state. Much more thinking needs to be done on this since it could be triggered by non-state actors...