Ever since the attacks of Sept. 11, 2001, officials in Washington and around the world have been warning of more devastating attacks from Islamic militants.
The warnings have been backed up by horrifying incidents. More than 200 people died in a bombing in Bali, Indonesia, in October 2002. A series of bombings in Madrid in March 2004 claimed nearly 200 more lives.
When there is an attack to rival those of Sept. 11, it may not be as dramatic -- but it could be even more deadly and disruptive.
Earlier this year, bioterrorism experts brought governmental leaders from around the world to Washington to take part in a "war game," exploring what would happen if such an attack occurred.
The participants included former Secretary of State Madeleine Albright, playing the U.S. president; Bernard Kouchner, former president of aid organization Doctors Without Borders, playing the French president; and Swedish Ambassador to the United States Jan Eliasson playing the Swedish prime minister. What follows is how it went.
Authorities will never know definitively, but they think the latest terrorist attack came in the chillingly simple form of one of the thousands of commuters who use New York City's bustling Penn Station.
The terrorist was probably equipped with a canister of smallpox the size of a small fire extinguisher, and infected 25,000 people in very little time. Terrorists with smallpox canisters were likely sent to other crowded hubs around the world, such as Istanbul's Grand Bazaar and Germany's Frankfurt Airport, multiplying the damage.
At first, the officials had no idea how many cases would develop. Soon, news broadcasts from several European countries reported outbreaks. Germany announced the formation of special isolation wards in Frankfurt hospitals.
Smallpox was one of the most-feared diseases in history. In the 20th century alone, it had killed 300 million people. But in the 1970s, it was eradicated. There was no way the new cases could be naturally occurring. Authorities knew it was terrorism immediately.
An al Qaeda splinter group claimed responsibility. Doctors struggled to find those who were infected as quickly as possible. But there were no rapid diagnostic tests available.
The world community began to take precautionary measures. They started what is called a ring vaccination program -- first inoculating those most likely to become infected, like health workers and port workers.
Initially, the leaders were told there were 51 reported cases worldwide, and there would be 10,000 in a month.
But then Turkey demanded help from its NATO allies to cover its population of 70 million people. The situation quickly got complicated.
After 9/11, the Bush administration ordered production of more than 300 million doses of smallpox vaccine, one for every American. It would be politically difficult to justify putting any Americans in harm's way without reason.
The U.S. president used the call for help to leverage future cooperation. "When we really needed help in Iraq, many of you decided it was not useful," she said.
The world leaders were informed there were more than 700 million doses of the smallpox vaccine available.