After alleged hackers in China compromised the personal e-mail accounts of top-notch American officials, military personnel and journalists, the world attention has shifted to cyber warfare and similar attacks that have happened in the past.

The revelation from web giant Google came only a week after Lockheed Martin Corp, a major defense contractor to the US government, announced last week that it was subject to an attack on its information systems network.  

This is not the first time that China comes under the hammer for alleged cyber attacks. Chinese hackers had been accused of launching a significant cyber attack on two Canadian economic ministries in February this year.

Although officials were successful in protecting sensitive information from the attackers, the Canadian government was concerned by the fact that the hackers were after financial records. Canada's spy service had reportedly been complaining about industrial espionage by the Asian nation.

Even Iran reported an attack on its nuclear programme in January this year. A virus named Stuxnet allegedly destroyed around 100 centrifuges. The centrifuges were inevitable components in the production of nuclear fuel at the Uranium enrichment facility in Natanz.

Although Iran claimed that the malware was neutralized in quick time, it was believed to have caused serious damage. Tehran accused Israel and U.S. for collaborating in the attack on its nuclear facility. Experts in the field have also opined that only a foreign state can unleash such a complex virus as Stuxnet.

A few months later, in April, Iranian experts claimed they had discovered a second virus dubbed as 'Stars', alleged to be an 'espionage virus'.  A senior Iranian official admitted after the attack that the virus was camouflaged in such a way that they could easily be mistaken for executive files of governmental organisations.

South Korea was also victim to an attack that happened in March this year. Hackers shut down many servers, some of which were run by the South Korean government. Although it was not that destructive, it adversely affected the business community. Very recently, the Seoul administration criticized North Korea for carrying out an attack on one of its leading banks.

The 2007 cyber attack on Estonia jeopardized the country's Internet infrastructure and brought the country's mobile phone networks to a halt. Although Estonia pointed fingers at Russia, Moscow was not willing to take the blame. Later, a Russian political analyst sparked off a controversy by claiming that it was his associate who masterminded the attack.

With the frequency of cyber attacks on governments and large corporations on the rise, military establishments like Pentagon are looking to take urgent measures. Sources suggest that Pentagon has already finished drafting its first  official computer sabotage strategy after the recent breach at Google.

Pentagon has maintained that cyber attacks on the country will be treated as an act of war. Sending a clear message to the Chinese perpetrators, Pentagon officials went on to suggest that US could opt for military retaliation. The Wall Street Journal quoted an official as saying ''If you shut down our power grid, maybe we will put a missile down one of your smoke stacks''.