Spies 'infiltrate US power grid

The US government has admitted the nation's power grid is vulnerable to cyber attack, following reports it has been infiltrated by foreign spies.

The Wall Street Journal (WSJ) newspaper reported that Chinese and Russian spies were behind this "pervasive" breach.

It said software had been left behind that could shut down the electric grid.

"The vulnerability is something [we] have known about for years," said US Homeland Security Secretary Janet Napolitano.