The paper explores the notion of cyber attack as a concept for understanding modern conflicts. It starts by elaborating a conceptual theoretical framework, observing that when it comes to cyber attacks, cyber war and cyber defense there are no internationally accepted definitions on the subject, mostly because of the relative recency of the terms. The second part analyzes the cyber realities of recent years, emphasizing the most advertised cyber attacks in the international mass media: Estonia (2007) and Georgia (2008), with a focus on two main lessons learned: how complicated is to define a cyber war and how difficult to defend against it. Crucial implications for world’s countries and the role of NATO in assuring an effective collective cyber defense are analyzed in the third part. The need for the development of strategic cyber defense documents (e.g. NATO Cyber Defense Policy, NATO Strategic Concept) is further examined. It is suggested that particular attention should be paid to the development of a procedure for clearly discriminating between events (cyber attacks, cyber war, cyber crime, or cyber terrorism), and to a procedure for the conduct of nation’s legitimate military/civil cyber response operations.