Futuristic fantasy? Not necessarily - cyber-warfare is fast becoming a fact of military life.

Scientific advances have opened the possibility of longer, better lives. They have also given the enemies of freedom new opportunities

Bill Clinton

The kind of disruption once possible only with a battery of intercontinental missiles now seems achievable at the click of a mouse.

Cyber-wars might not directly spill blood, but in the information age stemming the flow of data using so-called "weapons of mass disruption" can be as effective a way of bringing a country to its knees as bombing its oil refineries.

Sitting target

As our wired world becomes more reliant on technology for its prosperity and security, so it becomes increasingly vulnerable.

Thomas Siebel, chief executive of Siebel Systems, a provider of e-business software, says recent examples of prominent websites being shut down by young and relatively amateur hackers show how exposed the system is.

Electronic arsenal

Low-tech email "spamming" to clog networks "Logic bombs" activated at will to scramble enemy networks Fast-breeding "worm viruses" Trojan horse viruses designed to trace passwords Video morphing to push artificially generated images on to enemy TV stations

"If you want to shut down the free world", he says, "the way you would do it is not to send missiles over the Atlantic Ocean - you shut down their information systems and the free world will come to a screeching halt.

"If a college kid can do it, imagine what Libya and red China can do."

In geostrategic terms, the US is still very much the uncontested superpower based on its arsenal of conventional weapons. But on the electronic front, the field is much more fluid and the internet could prove to be the great leveller.

Arms cache

Unsurprisingly, the US is thought to hold one of the most sophisticated and top secret stores of so-called cyber-bombs.

The latest lethal weapon?

But that by no means gives it a monopoly.

In capable hands, a powerful computer hooked up to the web has the potential to be a relatively cheap, fast and effective tool of war.

During the Kosovo war, US officials are reported to have decided against deploying their electronic arsenal because of fears that the impact on civilian life would have led to charges of war crimes under the Geneva Convention.

The revelation highlighted a growing debate over the impact of these weapons on the nature of warfare and legitimate targets.

Potential targets are not only government computers but the lifelines that we all take for granted - our power grids, water and transportation systems

George Tenet Director Central Intelligence Agency

Late last year, Russian diplomats warned that the uncontrolled development of cyber-warfare applications "might lead to an escalation of the arms race".

There is also the genie-in-the-bottle syndrome to think about.

Once a cyber-attack has been unleashed, who's to say that in the interconnected world your carefully constructed virus won't spread to the networks of friendly or neutral nations?

The art of war

Intelligence analysts say one of the first concerted cyber-attacks occurred in Sri Lanka in 1997 in support of the Tamil Tiger separatists.

Sophisticated more in terms of organisation than technology, the strike was intended to disrupt government communications by overloading - i.e. spamming - Sri Lankan embassies with millions of e-mails.

Burma's military government has built a sophisticated cyber-warfare division

A year later, the Indian army's website on Kashmir was "hijacked" by supporters of Pakistan's claim to the disputed territory, who plastered the site with their own political slogans.

In Burma, the military government is believed to have built up an advanced cyber-warfare department within its own secret police force.

Using monitoring equipment loaned by the government of Singapore, analysts say the junta has been able to track online critics of the regime. A growing number of exiled activists say they have received viruses attached to e-mails later found to have been sent by Burmese agents.

And during the East Timorese crisis last year, independence leader Jose Ramos Horta threatened to unleash a series of viruses against Indonesia's banking sector if the government tried to rig the territory's referendum.

But military officials say these are just tips of the electronic iceberg.

Hack attack

According to US Government reports, at least 120 groups or countries are developing information-warfare systems, most of them using the net as their means of attack.

Already the US Defence Department is engaged in an ongoing war to protect its communications network.

US forces held back from using electronic weapons during the Kosovo conflict

Backed by a $1.4bn presidential budget, the Pentagon announced last October that it was consolidating offensive and defensive cyber-warfare programs under the authority of the US Space Command in Colorado Springs.

It says hackers try to penetrate its systems between 60 and 80 times a day, but analysts believe the real figures are likely to be much higher.

Most hackers gain access through so-called "back-doors" - a kind of electronic loophole which only tends to become apparent after the intruder has made their presence felt and left.

Once you've been infiltrated, you then have to trace who attacked you - a task complicated by the array of electronic "screens" available to hackers to mask their locations.

By then, of course, it could already be too late - a fact that is causing senior White House officials to contemplate the possibility of an "electronic Pearl Harbor".

Maybe the first shots of the global cyber-war have already been fired. Trouble is, if and when the war starts for real, you won't see it until it's too late.