Cyber warfare involves actions by a nation to penetrate another nation's computers or networks to cause damage or disruption across military, economic, political and social systems. While some experts argue for counterattacks in response to cyber harm, attribution of attacks is challenging due to spoofing of technical data. Existing international law does not fully cover cyber warfare. Other-than-internet attacks using vectors like USB devices or altered hardware present new ethical issues for policymakers seeking to prevent attacks while maintaining legitimacy of responses. A workable international treaty on cyber warfare will likely not be possible for over a decade.