Terrorism is a hazard to human life and material prosperity that should be addressed in a sensible manner whereby the benefits of actions to contain it outweigh the costs. Foreign-born terrorists who entered the country, either as immigrants or tourists, were responsible for 88 percent (or 3,024) of the 3,432 murders caused by terrorists on U.S. soil from 1975 through the end of 2015. This paper presents the first terrorism risk analysis of the visa categories those foreign-born terrorists used to enter the United States.

Including those murdered in the terrorist attacks of September 11, 2001 (9/11), the chance of an American perishing in a terrorist attack on U.S. soil that was committed by a foreigner over the 41-year period studied here is 1 in 3.6 million per year. The hazard posed by foreigners who entered on different visa categories varies considerably. For instance, the chance of an American being murdered in a terrorist attack caused by a refugee is 1 in 3.64 billion per year while the chance of being murdered in an attack committed by an illegal immigrant is an astronomical 1 in 10.9 billion per year. By contrast, the chance of being murdered by a tourist on a B visa, the most common tourist visa, is 1 in 3.9 million per year. Any government response to terrorism must take account of the wide range of hazards posed by foreign-born terrorists who entered under various visa categories.

The federal government has an important role to play in screening foreigners who enter the United States, and to exclude those who pose a threat to the national security, safety, or health of Americans. This terrorism risk analysis of individual visa categories can aid in the efficient allocation of scarce government security resources to those categories that are most exploitable by terrorists. The hazards posed by foreign-born terrorists are not large enough to warrant extreme actions like a moratorium on all immigration or tourism.