Recent cyber attacks on corporations and the growing use of malicious software to crack government servers and other vital installations have risen in past years. In response, the Pentagon has concluded that computer sabotage from another country constitutes as an act of war. This means that the Pentagon could potentially retaliate with traditional military hardware which includes a vast array of weapons at its disposal. Of course, not every cyber attack will have this serious of a retaliation – the Pentagon says that only attacks that could potentially threaten lives, or do as much damage and destruction as a traditional military attack would be liable for retaliation.
Source: WSJ