Of course, it could happen. It is not actually impossible. That is the reality of modern terrorism: it could strike anywhere. But it did seem spectacularly unlikely. That school was more under threat from a tornado or a fire (or a rampage by its own pupils) than an al-Qaeda terror gang. Yet it was the terrorist threat that kept this woman afraid.

But that is no accident. It is the result of policy. A book on terrorism went on sale in America this week. It is called The One Percent Doctrine and was written by Ron Suskind. The title comes from a principle articulated by Vice-President Dick Cheney (or Darth Cheney as liberals call him) that stated a one percent chance of terrorists getting a weapon of mass destruction should be treated as if it were a certainty.

Now as security policy that's not a bad idea. The threat from terrorists, as 9/11 so awfully proved, is all too real. There is much to be said for security forces using the one percent principle and little to be said for them being overly cautious. It's been said, and rightfully so, that to stop a threat, they have to succeed every time. The terrorists have to be lucky just once.

The problem is this overkill attitude has seeped into the mainstream. A culture of fear has entered into American public and private life, especially because there is a lot of money to be made out of it. One sees it in the unseemly scramble to get money from the Department of Homeland Security. Newspapers in New York bleat that their city needs more money than towns in states like Iowa or Nebraska. Back in those states local politicians demand their own fair share.

Now, obviously, some places are more at risk and therefore deserve more money for defence than others. But the debate needs to be based on common sense, worked out quietly by security professionals; not politicians and lobbyists engaged in a feeding frenzy with the scent of money in their nostrils.

Fear has also become a political football. One saw it in the row over the now defunct Dubai Ports deal. Democrats raced each other to cry wolf over a move that would have seen a firm from the United Arab Emirates take over the running of some major US ports. It worked too. Ignoring the opinion of actual security experts, Democrat politicians (and many Republicans) whipped up the idea of a terrorist threat and used it to bash the White House.

I found myself in the distinctly odd position of backing President George W Bush in a fight against the anti-Arab fear mongering of people like Hillary Clinton. But the sad lesson was that fear works politically. Bush's poll numbers slumped further and the deal collapsed. Democrats had just learned what Republicans have known for years. Fear is the political gift that keeps on giving.

But if fear has become a winning formula politically, it has also become a gold mine for business. There is much money to be made from scaring Americans and very little to be made from telling them to relax, enjoy their good fortune to be born in the USA and have a nice day.

Books on terrorism warn of imminent destruction. TV stations battle over ratings with ever more bizarre scare stories. Fear is a commodity whose value increases exponentially. Just look at the Department of Homeland Security. This newly created body, born of the war on terror, is a vast and enormous creature. It is already the third largest cabinet department and boasts 180,000 employees and a 2004 budget of $36.5bn. It is safe to say that, like all big bureaucracies, it fights its corner when it comes to getting resources. It does not do that by playing down any threat.

At the same time the war on terror has spawned a whole new consultancy industry made up for security experts, lobbyists and companies coming up with new technologies or ideas to make America safer. They bid for contracts from the Department of Homeland Security or try to persuade it to adopt their products. In short, they act like any other industry lobbying government for gold and treasure. But again, there is little money to be made in realistic analysis. Government officials are cashing in. More than 90 former government security experts have joined private security consultancies, lobbying their old employer for business.

Of course, all this is helped by the undeniable fact that terrorism is a genuine threat. Terrorists could let off a dirty bomb. Or take over an American high school. Or attack a shopping mall. Or a crowded restaurant. With the widespread availability of guns in the US such an attack would be simple. So simple that one wonders why it has not yet happened. Could it be that the threat, while real, is actually much, much less than all the books, journalists, lobbyists and politicians would have us believe? That far greater dangers to America's way of life lie, not in the schemes of Osama bin Laden, but in the environment, dependence on oil, huge debts and the rise of China. I would say yes. But there is not much profit to be made out of saying that.

The law enforcement official told The Associated Press the seven were mainly Americans with no apparent ties to al-Qaida or other foreign terrorist organizations. He spoke on condition of anonymity so as not to pre-empt the news conferences.

"There is no imminent threat to Miami or any other area because of these operations," said Richard Kolko, spokesman for FBI headquarters in Washington. He declined further comment.

Residents living near the warehouse said the men taken into custody described themselves as Muslims and had tried to recruit young people to join their group. Rose said they tried to recruit her younger brother and nephew for a karate class.

She said she talked to one of the men about a month ago. "They seemed brainwashed," she said. "They said they had given their lives to Allah."

Residents said FBI agents spent several hours in the neighborhood showing photos of the suspects and seeking information. They said the men had lived in the area for about a year.

Benjamin Williams, 17, said the group sometimes had young children with them. At times, he added, the men "would cover their faces. Sometimes they would wear things on their heads, like turbans."

A man who called himself Brother Corey and claimed to be a member of the group told CNN late Thursday that the individuals worship at the building and call themselves the "Seas of David."

He dismissed any suggestion that the men were contemplating violence. "We are peaceful," he said. He added that the group studies the Bible and has "soldiers" in Chicago but is not a terrorist organization.

Xavier Smith, who attends the nearby United Christian Outreach, said the men would often come by the church and ask for water.

"They were very private," said Smith, 33.

FBI Director Robert Mueller, questioned about the case on CNN's "Larry King Live," said he couldn't offer many details because "it's an ongoing operation."

"We are conducting a number of arrests and searches" in Miami, Mueller said, which were expected to be wrapped up Friday morning.

Managers of the Sears Tower, the nation's tallest building, said in a statement they speak regularly with the FBI and local law enforcement about terror threats and that Thursday "was no exception."

Security at the 110-floor Sears Tower, a Chicago landmark, was ramped up after the Sept. 11 attacks, and the 103rd-floor skydeck was closed for about a month and a half.

"Law enforcement continues to tell us that they have never found evidence of a credible terrorism threat against Sears Tower that has gone beyond criminal discussions," the statement said.

The warehouse owner declined comment. "I heard the news just like you guys," George F. Mobassaleh told the AP. "I can't talk to you."

Several terrorism investigations have had south Florida links. Several of the Sept. 11 hijackers lived and trained in the area, including ringleader Mohamed Atta, and several plots by Cuban-Americans against Fidel Castro's government have been based in Miami.

Jose Padilla, a former resident once accused of plotting to detonate a radioactive bomb in the U.S., is charged in Miami with being part of a support cell for Islamic extremists. Padilla's trial is set for this fall.

The document says that Batiste "recruited and supervised individuals in order to organize and train for a mission to wage war against the United States government, which included a plot to destroy by explosives the Sears Tower in Chicago, Illinois," the nation's tallest building.

Batiste gave the undercover agent a list of equipment he needed to "wage jihad" including "boots, uniforms, machine guns, radios and vehicles," according to the document, as well as bullet-proof vests and $50,000 in cash.

"In order to obtain funding and support for the mission to wage war against the United States, Narseal Batiste and other conspirators attempted to obtain the support of al Qaeda," the document said.

"... the conspirators pledged an oath to al Qaeda and supported a purported mission of al Qaeda to destroy FBI buildings within the United States," it said.

Batiste and Burson Augustin gave the undercover agent photos of Miami's FBI building; photos and video of the James Lawrence King Federal Justice Building, federal courthouse buildings, the Federal Detention Center and the Miami Police Department; all in Miami-Dade County, according to the indictment.

Five of the suspects were arrested in FBI raids Thursday in Miami and one in Atlanta, Georgia. A seventh man was detained earlier. Some of the suspects were expected to appear in federal court Friday afternoon.