Britain faces a "real and credible" threat from cyber attacks by hostile states and criminals, and government systems are targeted 1,000 times each month, the head of UK's communications spy agency says.
Iain Lobban, the director of the Government Communications Headquarters (GCHQ), said such attacks threatened Britain's economic future and added some countries were already using cyber assaults to put pressure on other nations.
"Cyberspace is contested every day, every hour, every minute, every second," he said in a rare speech which was published on Wednesday.
The internet lowered "the bar for entry to the espionage game", he said, and its expansion increased the risk of disruption to Britain's critical infrastructure, such as power stations and financial services.
"The threat is a real and credible one," said Mr. Lobban, whose GCHQ agency, a big eavesdropping operation similar to the National Security Agency in the United States, handles operations such as intelligence-gathering and code-busting.
Politicians and spy chiefs in Britain and around the world have increasingly been warning about the growing cyber threat.
The issue came to the fore last month when security experts suggested that the Stuxnet computer worm that attacks a widely used industrial system could have been created by a state to attack nuclear facilities in Iran.
"It is true we have seen the use of cyber techniques by one nation on another to bring diplomatic or economic pressure to bear," Mr. Lobban told the International Institute for Strategic Studies, without giving specific details.
A recent parliamentary report said GCHQ had indicated that states such as Russia and China posed the greatest threat of electronic attack on Britain.
The United States is currently setting up a Cyber Command to defend defence networks and mount offensive cyber strikes, and Mr. Lobban said there needed to be agreement on the "proper norms of behaviour for responsible states in cyber space".
He said worms had already caused significant disruption to British government systems, with 20,000 malicious emails on networks every month, 1,000 of which were deliberately targeted.
With 100 billion pounds of tax and benefit payments due to be processed online over the next few years, he warned that it would be a major challenge for government to avoid putting personal data at risk or being open to fraud.
He said the growth of electronic crime was "disturbing", costing the economy billions of pounds, and added there had been theft of intellectual property on a massive scale.
Details of the government's Strategic Defence and Security Review, along with a Treasury spending review, are to be published next week and Mr. Lobban said ministers would be looking at areas that needed investment and to be prioritized.
"Just because I, as a national security official, am giving a speech about cyber, I don't want you to take away the impression that it is solely a national security or defence issue," he said.
"It goes to the heart of the our economic well-being and national interest."