The United States have tested their vital infrastructure, including power grids and banking systems, with a simulated attack. This security exercise was called Cyber Storm and it lasted for a week long, BBC reports.
The attack drew 115 agencies, this included the FBI, CIA and also agencies like the Red Cross.
Other parties that played a role where IT companies and state and foreign governments.
The exercise had given the US "an excellent opportunity to enhance our nation's cyber security," the US said.
"Cyber security is critical to protecting our nation's infrastructure," George Foresman of the Department of Homeland Security added in a statement.
The US has been accused of being unprepared for a determined attack by hackers.
Cyber Storm reportedly not only tested against attacks by hackers, but also by bloggers - who deliberately spread misinformation in the exercise.
There was no effect on the Internet, as the attack was carried out on secure computers in the basement of the Secret Service in Washington DC.