What are the different categories of cyber warfare?

There are several levels of cyber war, of which three stand out: cyber war as an adjunct to military operations; limited cyber war; and unrestricted cyber war.
In effect, the first form of cyber warfare focuses almost exclusively on military cyber targets. In a limited cyber war, the information infrastructure is the medium, target and weapon of attack, with little or no real-world action accompanying the attack.
An unrestricted cyber campaign would almost certainly be directed primarily against the target country's critical national infrastructure: energy, transportation, finance, water, communications, emergency services and the information infrastructure itself. It would likely cross boundaries between government and private sectors, and, if sophisticated and coordinated, would have both immediate impact and delayed consequences. Ultimately, an unrestricted cyber attack would likely result in significant loss of life, as well as economic and social degradation.
(Countering cyber war, NATO Review - Vol. 49 - No 4 - Winter 2001) http://www.nato.int/docu/review/2001/0104-04.htm