In the overheated rhetoric of Chinese military strategists, it is known as the assassin's mace -- an expression that refers to an unconventional weapon or strategy whose impact is so unexpected and unpredictable that it can tilt the balance of war in favour of the weaker combatant. The Chinese assassin's primary target is the United States. The assassin's weapon, however, relies more on intrigue and technological sabotage than brute force. Earlier this month, American officials, speaking off the record to the Financial Times, disclosed that hackers connected to the Chinese People's Liberation Army had successfully penetrated a Pentagon computer network. The online raid offered a glimpse into the growing importance of cyberwarfare, China's newest assassin's mace.

Germany has also accused the People's Liberation Army of hacking into its networks, and Britain admits that attempts to penetrate its networked systems are a growing problem. In fact, most developed countries are widely assumed to engage in cyberespionage, which refers to the extraction of sensitive information from the networked systems of governments and private businesses -- accomplishing what traditional spies once did without the trouble of risking capture, or straying far from a computer terminal. "That's the beauty of the Internet," says James Lewis, a senior fellow at the Center for Strategic & International Studies in Washington. "Twenty years ago, you had to send somebody to skulk around in bars outside the plant gates and hope you could recruit someone. Now you can do it remotely."

Cyberwarfare is a step beyond espionage. It involves disabling or corrupting an adversary's computer systems. This spring, for example, Estonia accused Russia of cyberattacks that crippled bank and government computers following a dispute between the two nations about a Russian war memorial in the Estonian capital. Russia has also been accused of cyberattacks against Ukraine, while South Korea has alleged that North Korea has trained 600 hackers for attacks not only against it but also the U.S. and Japan.

It is China that is the most aggressive -- and perhaps least discreet -- about its efforts to exploit cyberwarfare's potential. This is because cyberattacks are seen as valuable weapons in asymmetric warfare, meaning a contest between unevenly matched opponents. "China is convinced that, financially and technologically, it cannot defeat the United States in a traditional force-on-force matchup," reported the U.S.-China Economic and Security Review Commission in testimony to Congress this June. "As evidenced by the trajectory of its military modernization, Chinese defence planners are seeking to accomplish the goal of undermining the U.S. military's technological edge through a variety of disruptive means. Among these is cyberwarfare."

The cyberwarfare envisioned by the Chinese would entail more than the online vandalism directed against Estonia. Some analysts point to what James Lewis calls the "Godzilla scenario," in which a country's entire infrastructure is targeted, banks, airports and communications networks are shut down, and public order disintegrates. The chances of such a scenario unfolding are remote. It is unlikely that the Chinese, or any other state, have the capability to unleash such damage, and doing so would only be useful in a total war.

A real conflict between China and the United States, however, would almost certainly be a limited one fought over Taiwan, an American ally that China views as a breakaway province to be "reunified" with the rest of China. The United States has pledged to assist Taiwan should China invade. But geography favours the Chinese. Taiwan lies just off the coast of China but is separated from the United States by the Pacific Ocean. In any war with China, Taiwan's strategy will be to hold out until U.S. forces arrive. China's strategy is to delay that arrival long enough to force Taiwan to negotiate its capitulation.

James Mulvenon, director of the Center for Intelligence Research and Analysis, which does contract research for the American intelligence community and the Department of Defense, says that the Chinese have probed American military networks and concluded that attacking them can cause the most damage when forces are being marshalled and sent to a conflict zone. "If you allow the U.S. military to get locked and loaded on your border with the full-force protection package, it's over," he said in an interview with Maclean's. "The U.S. military is just going to pick apart your command and control network, and it's going to be ugly. But the vulnerability is in that deployment phase."