A cyber attack that originated from the Chinese city of Jinan that selectively targeted key government officials in the U.S. and its allies has focused uneasy limelight on China, even as the western governments are tinkering with their military rule books to call cyber attacks 'acts of war'.

Chinese hackers broke into the personal Gmail accounts of senior officials and military personnel of the U.S. government and it allies and stole sensitive data, Google revealed on Wednesday, setting the stage for an era of heightened cyber tension between the world's top military powers.

Hackers 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.

The hack attack came to light just a day after it was revealed that the U.S. government was planning to bring in legislation declaring cyber attacks as acts of war.

The latest hack attack, which might bring Google and the Chinese administration into a fresh fist fight, was precisely planned and executed, raising doubts if the Chinese state had authorized it.

Britain's Guardian has reported that the sophistication of the attacks and their highly targeted nature eliminates direct financial gain as a motive. Google has not ruled out the chances of a state-sponsored hack attack. The report says there is no evidence suggesting that the cyber criminals were in Chinese government payrolls.

However, there have been serious allegations against the Chinese state machinery in the past over cyber attacks on the U.S. and allies. Experts have said in the past that, for China, cyber warfare fits into the scheme of things.

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.

Sneaking into the email systems of high-profile sensitive targets could be just a precursor to daring attacks on critical computer networks supporting a country's security. The U.S. has realized the scope and gravity of cyber attacks and their utility in real warfare.

That is why the U.S. decided 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.

According to the Pentagon, planned retaliatory strikes against cyber criminals can come within the gamut of laws governing armed conflict. When an enemy deals a crippling blow to the country's assets by means of a cyber attack, it can be considered as an act of war.

When warranted, the US will respond to hostile acts in cyberspace as we would to any other threat to our country, the White House said a fortnight ago.

According to the US, the country's nuclear reactors, pipelines and mass transport systems are especially vulnerable. The US is vulnerable to sabotage in defence, power, telecommunications, banking. An attack on any one of those essential infrastructures could be as damaging as any kinetic attack on US soil, said former Pentagon cyber expert Sami Saydjari, according to the Guardian.

The U.S. military is also on high alert for possible hack attacks, especially by Chinese and Russian hackers.

The latest Gmail hackers, who launched the attack from Jinan in Shandong province, tried to take total control of the targets' gmail, including login details, settings, mail forward patterns and other functions.

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.

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.