RELENTLESS assaults on US computer networks by governments, hackers and criminals have created an urgent need for safeguards to protect these vital systems. Officials and experts have warned about cyber-security dangers for years; now the alarms are more insistent.

On Thursday, Gen Keith Alexander, the chief of the US Cyber Command and the director of the National Security Agency, said intrusions against computers running essential infrastructure increased 17-fold from 2009-11 and that it is only a matter of time before an attack causes physical damage. He has also called the loss of industrial information through cyber-espionage "the greatest transfer of wealth in history". Hundreds of companies, defence contractors and government agencies have been affected. There were 200 cyber-attacks on power plants, electric grids, refineries, transportation networks and water treatment systems last year.

Yet defences are thin. On a scale of one to 10, Alexander rated preparedness for a large-scale cyber-attack as "around a three". It is time for the endless talk of cyber-threats to be met by action. New York, August 1