An official with Brazil's electricity regulator has confirmed that large scale blackouts in 2005 and 2007 were caused by people hacking into the computers that control the electricity grid.

The official with ANEEL, which regulates electricity producers and transmission in Brazil, said that while the evidence was not absolute, it was widely believed that hackers broke into control computers and shut down power to millions.

The 2005 attack in Espirito Santo state shut off power to about four million people.

Another attack in 2007 shut off power to about one million residents in Rio de Janeiro.

The perpetrators were never identified.

Australian authorities are also concerned about such attacks.

The office of Attorney General Robert McClelland has a special advisory group to monitor progress in protecting infrastructure such as power grids.