"Innovations, both technological and organizational, over the last few decades have created a potential for non-obvious warfare, in which the identity of the warring side and even the very fact of warfare are completely ambiguous. The Stuxnet computer worm is only the most recent widely publicized example. This worm is believed to have infiltrated Iran's Natanz centrifuge facility, causing equipment to destroy itself over a period of weeks and leading to the premature retirement of 10 percent of Iran's uranium enrichment capability. Within several months of the worm's public disclosure (September 2010), Western intelligence sources announced that the earliest date Iran could build a bomb had been pushed back several years. Until the worm was discovered and dissected, the Iranians were uncertain why their equipment wore out so fast. Indeed, when confronted publicly with the possibility, they first denied that any such attack had happened, only to reverse themselves obliquely two months later. Although non-obvious warfare can be epitomized by cyber warfare, states can attack one another in many ways without the victim being certain exactly who did it or even what was done. Some, like electronic warfare (against nonmilitary targets) and space warfare, have yet to materialize in any strategically significant way. Others, such as naval/ land mining or sabotage, have long historical antecedents. What they share is ambiguity."
Air University: http://www.au.af.mil/au/
Strategic Studies Quarterly (Fall 2012), v.6 no.3, p. 88-101