The United States is fighting wars of attrition in Afghanistan and Iraq and chasing al-Qaeda's terrorist shadow across the globe, but it is a very different kind of warfare that keeps the Pentagon's No. 2 man William Lynn awake at night.
Cyber warfare, a battlefield without sovereign borders and populated by non-traditional foes, is the new frontier in which the US and allies such as Australia are wrestling to maintain their defences and identify their adversaries. For Mr Lynn, the US Deputy Secretary of Defence, it is unclear whether China, the rising superpower, is an ally or an adversary.
''The jury is still out … We would like to see China, given the strength of its economy and importance the nation plays in the world stage, be a constructive actor in the cyber arena as in every other way. It's very important to the success of any countering of the cyber threat that they do play that role,'' Mr Lynn said, in an interview with the Herald in Sydney.
The US internet giant Google said last month that it had been subject to cyber attacks originating in China. Many believe these were carried out by hackers under the direction of Chinese security forces. The US Secretary of State, Hillary Clinton, called on China to investigate the Google intrusions.