The US, UK, China and Russia are among 15 nations that have agreed to work together to reduce the threat of cyber attacks.
The agreement, signed at the UN, represents a significant change in US posture, said Robert Knake, a cyberwarfare expert with the Council on Foreign Relations.
Participation of the US demonstrates the Obama administration's strategy of diplomatic engagement, he said.
The group has recommended the UN creates norms of accepted behaviour in cyberspace. It should also exchange information on national legislation and cybersecurity strategies, and strengthen the capacity of less-developed countries to protect their computer systems.
When the group last met in 2005, they failed to find common ground. This time, by crafting a short text that left out controversial elements, they were able to reach a consensus.
In the past, US efforts to work with other countries in cyberspace have centred on combatting crimes online, but did not deal with issues such as state involvement in or responsibility for cyber intrusions into critical computer systems.
Others in the group are France, Germany, Estonia, Belarus, Brazil, India, Israel, Italy, Qatar, South Korea, and South Africa.