The US Department of Homeland Security (DHS) is failing to secure vital internet infrastructure, an American government organisation has warned.

The Government Accountability Office said in a report that the US is unprepared for emergencies. A PDF of the report can be downloaded here.

"While the DHS has initiated multiple efforts to fulfil its responsibilities, it has not fully addressed any of these responsibilities and much work remains ahead," the report stated.

Such responsibilities range from developing a plan to protect America's crucial infrastructure, to strengthening international cyber-space security.

"The DHS cannot effectively function as the cyber-security focal point intended by law and national policy," the report concluded.

"As such, there is increased risk that large portions of our national infrastructure are either unaware of key cyber-security risks, or are unprepared to effectively address cyber-emergencies."

The DHS was created in November 2002 in response to the terrorist attacks of 11 September 2001, creating a single government body to oversee several security agencies.

The failing grade comes amid a major exercise to simulate an electronic attack against the US. The test was conducted by the CIA.