On October 9th, commuters waiting for their trains at a subway station on the outskirts of Washington DC saw a man releasing a clear spray from a bottle. Within minutes, the symptoms started to appear. Thirty-five people felt sick in the same way - nausea, headache, and sore throat. What was the cause? Nerve gas, like the sarin released in the Tokyo underground in 1995 by the Aum Shinrikyo cult? Anthrax?
The deadly substance was neither a chemical nor a biological weapon. It was ordinary window cleaner of the kind that millions of house-proud citizens inhale every weekend without suffering any symptoms at all.
More pertinently, what the commuters were inhaling was pure, unadulterated terror. Like the 17 people who were taken to hospital from a school in Washington State a few weeks earlier after the smell of fresh paint provoked panic, or the thousand students who deluged medical centres in Manila with flu-like symptoms after rumours of a biological attack spread via text messages, they were experiencing the effects of the most potent and virulent virus of all: fear.
In the hours after the stunning attacks of September 11th, journalists and commentators reached for two sweeping generalisations. The world would be a very different place. The terrorists must not be allowed to win. One has been very clearly borne out by subsequent events. The other has proved to be a spectacular case of missing the point.
The point is that the reason the world has become a very different place is that the terrorists have won. They achieved everything they might have hoped for, and more than they could have reasonably expected.
From Maryland to Manila, from Navan to Nairobi, they have planted seeds of panic that will blossom for years to come. Or to use a metaphor appropriate to the situation of Irish people looking over their shoulders at Sellafield, they have created a fast-breeder reactor in which a flick of the switch produces a massive chain of potentially explosive events.
Their achievement on September 11th was to create a psychological context in which even relatively small events will be endlessly enlarged by the magnifying glass of mass alarm. In the world before September 11th, the threat of chemical or biological attacks was just part of the background noise of global modernity. Our collective consciousness filtered it out.
Incidents of greater import than the current anthrax scare had far less impact. In 1984, 700 people in Oregon went down with a potentially fatal strain of salmonella because a cult had deliberately infected salad bars. The story was soon forgotten.
In the 1990s, sarin nerve gas was released in significant quantities accidentally in Baghdad during the destruction of a chemical weapons plant, and deliberately on the Tokyo underground. The global impact was short-lived and minimal.
Now, because the terrorists have succeeded in creating an imaginative context in which people everywhere can connect their fears together, a very small campaign can have a huge impact. Just as the hijackers did on September 11th, when they turned familiar objects like planes into nightmarish messengers of doom, the people behind the anthrax scare have transformed an object that most people handle every day - an ordinary letter - into a potential carrier of plague.
They may or may not have known that local hoaxers would come to their aid all around the world. The sophistication they showed in targeting media organisations first makes it plausible to assume that they made an educated guess that an army of cranks was just waiting to be mobilised.
What is certain is that these are serious people, who understand that in the wake of one great spectacular, an economy of effort becomes possible. September 11th created a world in which any malevolent little grudge-bearer can close down a TV station, an airport, a postal sorting office, even the US House of Representatives, for the cost of a postage stamp.
Even in purely medical terms, the limited danger from a few spores of anthrax can create a genuine epidemic of long-lasting psychosomatic illnesses. In a thoughtful and considered article in the current issue of the British Medical Journal, British psychiatrist Dr Simon Wessely, an American public health strategist, Kenneth Craig Hyams, and an Australian sociologist, Robert Bartholomew, jointly predict such consequences.
The immediate effects, they say, will be physical symptoms like the incidents already recorded. In the longer term, "the general level of malaise, fear, and anxiety may remain high for years, exacerbating pre-existing psychiatric disorders and further heightening the risk of mass sociogenic illness".
Arguably, therefore, the real action in this war is on the home front. No amount of bombs dropped on Afghanistan will recreate the sense of security lost on September 11th.
Even the complete elimination of the Taliban regime is very unlikely to destroy either the global al-Qaeda network or the many similar groups that will be encouraged to step up the "holy war". No one knows better than we do in Ireland that once you have created a political narrative within which individual acts of violence can be interpreted, the rest is easy to sustain and almost impossible to stop. You can't stop a man with a machine gun walking into a crowded bar. You can't stop a man with a car, as Dubliners learned on Thursday, ploughing his way through a crowded city street.
The awful truth is that terrorism is quite easy. It is especially easy in open societies like the US or the European democracies. But even intensely militarised societies with a huge apparatus of surveillance and repression can't prevent it. The IRA never found it impossible to operate in South Armagh. The huge Israeli security machine couldn't stop a gunman walking up a cabinet minister this week and killing him. Russia's savage war on Chechen "terrorism", though often fought outside the rules of civilised democracies, hasn't stopped Chechens setting off car bombs.
Even giving up the openness that makes democracies democratic is not, therefore, the answer. Nor is it ultimately possible to fight a globalised, stateless network of terror by simply reverting to old habits and attacking states like Afghanistan and Iraq.
The only effective response in the long term is the incredibly expensive and difficult one of constructing global institutions of effective justice on the one hand and sorting out the political slums that breed such hatred on the other.
In the meantime, the most important thing states can do is to stop doing the terrorists' work of spreading the fear by themselves indulging in panic-stricken reactions. In practical terms, this means avoiding the kind of measures that make far more people sick with worry than they actually protect from the threat of biological attack.
The authors of the BMJ article, for example, question current proposals to install detectors to identify chemical warfare agents on the Washington DC subway system. They point out that when these detectors were used during the Gulf War, there were 4,500 false alarms, creating at least as much fear as an actual attack would have done.
It might also help not to exaggerate the threat to suit a political agenda. The anthrax scare, for example, has been magnified by suggestions from those who want to attack Iraq that the vile regime in Baghdad is behind it.
The former UN weapons inspector in Iraq, Scott Ritter - an American with no love for Saddam Hussein - pointed out in yesterday's Guardian that there is "no verifiable link whatever" with Iraq, and that politically-motivated suggestions to the contrary "merely fan the flames of fear and panic".
Those who want to stop those flames from becoming a conflagration would do well to reflect that nothing fuels paranoia more effectively than evidence that your own government is trying to hide the truth from you. Whether the propaganda machines being rolled out to fight the war for hearts and minds by censoring inconvenient evidence can countenance this reality is another question.