In one of the most blatant cyber attacks carried out against the United States by a foreign government, as many as 24,000 Pentagon files were stolen in March, US Deputy Secretary of Defense revealed on Thursday.

The sensitive files, which the unnamed rogue state's cyber attackers hacked into, belonged to a defense-industry-computer network, William Lynn said. The data were stolen in a single intrusion, he added.

Lynn said We have a pretty good idea who did it, but did not offer further clues. However, there has been relentless focus on Russia and China as potential enemies that could unleash cyber warfare tactics against the US.

According to Lynn, though most nation-states have sophisticated computer capabilities, they are deterred by the fearsome military power of the US. However, terror outfits and rogue states could still pose a threat. If a terrorist group gains disruptive or destructive cybertools, we have to assume they will strike with little hesitation, Lynn said.

The U.S. decided recently to change it military rule book to accommodate provisions for retaliatory strikes on hacker groups and their state sponsors if critical U.S. infrastructure, military installations or other national assets come under attack.

Many experts share the feeling that sophisticated cyber attacks can deal crippling blows on enemy states. The U.S. has decided to be up to speed with the developments, and that's why the Pentagon now considers cyber attacks on critical installations as acts of war.

In May Chinese hackers had broken into the personal Gmail accounts of senior officials and military personnel of the U.S. government and it allies and stole sensitive data. The revelation by Google had set the stage for an era of heightened cyber tension between the world's top military powers.

Defense Secretary Leon Panetta has said there was a strong likelihood that the next Pearl Harbor could be a crippling cyber attack on the U.S. power grid and financial and government systems.

The increasing focus of Chinese hackers on the U.S. and its senior officials and military sites increase the prospects of a worsening cyber warfare scenario.

Military strategists have long prognosticated that China could unleash cyber warfare to counter the technological and military advantage that the US has got. Some analysts have said that, for China, cyber warfare was a critical part of its strategy to face down the US threat. China has long regarded cyberwarfare as a critical component of asymmetrical warfare in any future conflict with the U.S. From China's perspective, it makes sense to use any means possible to counter America's huge technological advantage, the TIME magazine wrote in 2007.

It emerged in May that Chinese Gmail hackers had unleashed malware or phishing scam to highjack the accounts of government functionaries, military top brass and journalists in what appears to be a selective attack on key targets, especially political rivals of China, from where the cyber criminals launched their attack.

According to Britain's Guardian, the sophistication of the attacks and their highly targeted nature eliminates direct financial gain as a motive.