For the first time, the US has interpreted an existing treaty to include aggression in cyberspace as a trigger for international military cooperation.
The US and Australia issued a joint statement that says they both interpret the 1951 ANZUS Treaty among the US, Australia and New Zealand to mean that if one country suffers a cyberattack it will consult with the other in deciding how to deal with it.
In the past the treaty has resulted in Australia and New Zealand sending troops to help fight the Vietnam War and to supplement US military operations in Afghanistan.
While the treaty is still referred to as "Anzus", New Zealand's membership has effectively lapsed since the fourth Labour Government's nuclear ships ban in the 1980s.
This is the first cooperative international expression of the US tenet for cyberwarfare that says cyberattacks may warrant physical, military retaliation.
"This is the battlefield of the future," said US Department of Defense Secretary Leon Panetta, "and our ability to work together is extremely important to the challenge of being able to counter this very significant emerging threat."
The joint statement was issued by US Secretary of State Hillary Clinton and Panetta along with Australian Minister for Foreign Affairs Kevin Rudd and Australian Minister for Defence Stephen Smith.
It says in part that "in the event of a cyber attack that threatens the territorial integrity, political independence or security of either of our nations, Australia and the United States would consult together and determine appropriate options to address the threat."
The two governments "recognise the value of close collaboration with allies and like-minded nations on cyber issues, and are working together closely to address mutual threats and challenges emerging in and from cyberspace," the statement says.
"This represents a new operational dimension the US Alliance. It is appropriate we take this step on the 60th Anniversary of the Alliance," Rudd said in a written statement.
- Additional reporting by David Watson