A bomb threat is generally defined as a verbal or written threat to detonate an explosive or incendiary device to cause property damage or injuries, whether or not such a device actually exists. Typically delivered by phone, or other telecommunication means, the great majority of such threats are the result of pranks or other sociopathies. Criminal statutes typically dictate severe penalties. For example, the state of Massachusetts, U.S.A., provides for penalties of up to 20 years in prison, up to $50,000 fine, and restitution for the costs of the disruption.
Some statutory definitions include the threatened use, release or placement of other harmful agents, such as poisons, biological pathogens, radioactive materials, or even a dangerous weapon (e.g., aboard an airliner). Other statutes enhance the penalties for threats made against specific places or persons (e.g., government facilities or dignitaries), not to mention the actual possession of harmful devices or agents.
Many bomb threats that are not pranks are made as parts of other crimes, such as extortion, hijacking, or robbery. Actual bombings for malicious destruction of property, terrorism purposes or murder often occur without any warning, let alone threats.
The decision on whether or not to evacuate an area or building, depending on the perceived reliability of the threat, may be made by local controlling authorities or those in charge of the targeted facility based on advice from bomb disposal experts. In many cases, where there is a large facility involved, it is very difficult and time-consuming to ensure the absence of any bomb or other hazardous device or substance.