Many of the increasing number of Cyber War skirmishes have been fought by mercenaries, or just private individuals out to do some damage. A recent example occurred in Lithuania, after a law was enacted prohibiting the display of symbols dating from the time when the country was part of the Soviet Union. The Soviet period is much hated in Lithuania, but still admired by many Russians. So over 300 Lithuanian web sites were defaced by, apparently, pro-Soviet Russian hackers.
This sort of Cyber War waged by non-government groups is becoming more frequent. In some cases, when specific, and highly classified, data is taken, mercenary hackers are believed to be responsible (at least in some cases), and carrying out attacks paid for by a foreign government. It's better to use mercs, as that makes a nasty diplomatic situation, not to mention retaliation, less likely. But there are lots of skilled freelancers out there, who do not hesitate to make war on their own. This could become a serious problem, especially if people got killed (as in hacking a hospital or power plant), or some serious physical damage was done.
Controlling these privateers, who often work for criminal gangs, has proved difficult. The gangs are usually willing to work with the government, especially if some of their other cyber crime activities are ignored. But many of these hackers are virtually unreachable by the government.
I've written about this before. And here. There are other posts.
And these private warriors won't remain restricted to the Internet in the long run.
But also remember that in the long run, our state-centric monopoly on the use of military force is the exception and not the rule.
Say good bye to Westphalia.
