The Federal Bureau of Investigation (FBI) defines terrorism as "the unlawful use of force or violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives." 
Images of the attacks on the World Trade Center in New York, the Pentagon in Virginia, the plane crash in Pennsylvania, the Murrah Federal Building in Oklahoma City and the Olympic Centennial Park in Atlanta are hard to forget. 
These terrorist incidents caused thousands of deaths and injuries and billions of dollars in property losses. They also inflicted a huge emotional toll within the impacted communities and throughout the world. 
According to the FBI, sporting events, political conventions and other special occasions are attractive opportunities for domestic and foreign terrorists. 
Although bombing has been the most popular method used in recent terrorist incidents in the United States, terrorism can occur in several forms. In recent years, terrorists have used arson, hijackings and shootings to attain their political and social goals. 
Terrorists can also use chemical or biological agents. Because people may not become ill immediately after being exposed to a biological agent, it may take some time for government officials to determine that such an attack has occurred. 
In the event of an attack, government officials will instruct the public on what actions they should take. It’s important that you remain calm and cooperate fully with local officials. Failure to follow instructions from local officials could cost you and others their lives. 
In the event of a chemical or biological attack, instructions will be provided by local public health and safety officials on personal protection, decontamination and health warnings. Information will be provided via radio, television and the print media.