Cyberwars - in which one side takes out the other's economy and government by sabotaging its IT infrastructure - have two differences from standard wars.
The first is that cyberwars are deniable, as Vladimir Putin has demonstrated. He has attacked Estonia, our NATO ally, but denies that he has done anything of the sort. NATO does not wish to acknowledge that one of its members has been attacked, because this would impose an obligation of retaliation.
The second advantage is that cyberwars are asymmetric. A group of western hackers could hit the Russian government with or without a lead being taken by NATO.
In these days of asymmetric warfare, who is most vulnerable to such an attack? Plainly, western governments are more exposed than developing countries. They rely more on their IT infrastructure. On the other hand developed countries have better defences, more backup systems, and greater offensive resources.
A cyberbomb that totally destroyed IT systems - remember the discussion about the Millennium bug? - would damage western countries more than countries like Russia or Iran. But it seems intuitively unlikely that such a bomb could be created. It is more likely that even the most determined assault would only take out a portion of the infrastructure. And the internet was designed to resist just such an assault. It would slow down, but it would not stop working. Alternative routes for every message would still exist. The larger and more extensive systems would therefore be more resistant to attack.
Could a freelance group of hackers do NATO's job and hit back at Russia? Quite possibly. It would probably be illegal, and might be dangerous. But it could probably be done.