"Technologically capable nations are, perhaps by necessity, contemplating the addition of computer attack to their arsenals. During the Kosovo intervention, the United States attempted limited electronic attacks on Serbian computers containing banking records of Serbian leaders. The United States is not alone, however. In 1995, the National Security Agency and Department of Energy estimated that more than 120 nations already had some sort of computer attack capability. [...] The potential for such a crisis makes the application of computer network attack a very different sort of combat power than the kinetic weapons it may someday supplement or replace. Like kinetic weapons, a computer network attack can destroy both military and civilian targets. Unlike kinetic weapons, however, a computer network attack can reach across the world at the speed of light, invisibly transiting many international borders en route to its target. Like chemical and biological weapons, cyber weapons can target large masses of people in both military and civilian communities. Unlike biological and chemical weapons, however, they affect humans indirectly rather than directly. Cyber weapons thus share some similarities with weapons of yesterday, yet they occupy a completely new niche by their nature. [...] To use these weapons ethically and legally, commanders and staffs must weigh their use against classes of targets and in some cases against individual targets, using clearly enunciated interpretations of the doctrines of discrimination and proportionality. The most basic questions were posed clearly by a newspaper reporter: 'For now, many sticky questions must be considered: When is a cyber attack justified, what if it affects civilians, and is a cyber attack an act of war?'"
U.S. Army War College, Parameters: http://www.carlisle.army.mil/usawc/parameters/
Parameters: United States Army War College Quarterly (Spring 2001), v.31 no.1, p.44-58