A well-organized group of hackers (search) has engaged in an "industrial scale" attack designed to cull commercially and economically valuable data from vital computer networks across Britain, the government warned Thursday.

In one of its most high-profile warnings about sophisticated electronic attacks, the normally secretive National Infrastructure Security Coordination Center (search) said hackers believed to be from Asia have targeted parts of the country's "critical national infrastructure."

The attacks have been going on for several months and have involved the communications, energy, finance, health, government and transport sectors, the NISCC said. Most of the attacks have been against central government computer systems, though companies and individuals are also at risk, the agency warned.

"We have never seen anything like this in terms of the industrial scale of this series of attacks," NISCC Director Roger Cumming (search) said. "This is not a few hackers sitting in their bedroom trying to steal bank account details from individuals."

Determining the origin of the attacks was extremely difficult, the NISCC said. The agency said it had traced the attacks back to "the Far East" by analyzing the numeric Internet addresses stamped within e-mails.

Those addresses, however, can sometimes be faked, and e-mail sent from elsewhere might have been rerouted through Asian computers.

A spokesman for Britain's Home Office, which oversees the NISCC, said the agency was talking to authorities in a number of countries to investigate further, and the government believed it was inappropriate to comment further while that process was continuing.

"We are not aware of any loss of information," the spokesman said on customary condition of anonymity. "We can't be certain of that. That's part of the reason we are broadening our sphere of advice. We recognize we need some feedback to see how big this is."

The NISCC said attackers generally gained access to systems by sending e-mail to individuals who have jobs working with sensitive data.

The messages had subject lines that refer to news articles of interest to the recipient and a fake e-mail address to make it appear to come from a trusted contact.

The e-mails also contained an attachment or a Web link that, when clicked, secretly installs a rogue program, known as a Trojan, that allows the attacker to gain control of the recipient's computer remotely.

"Once installed on a user machine, Trojans may be used to obtain passwords, scan networks, exfiltrate information and launch further attacks," the agency said in its briefing urging all businesses to tighten security.

There have been high-profile hacker intrusions in the United States.

In one long-running operation, hackers traced to Russia were found to have been quietly downloading millions of pages of sensitive U.S. military data, including one colonel's e-mail inbox. During three years, most recently in April 2001, government computer operators watched as reams of electronic documents flowed from Defense Department computers, among others.

The NISCC said the latest attack appears aimed at covertly gathering and transmitting sensitive commercial information.