The potential for terrorist attacks against agricultural targets (agroterrorism) is increasingly recognised as a national security threat, especially after the events of September 11, 2001. Agroterrorism is a subset of bioterrorism, and is defined as the deliberate introduction of an animal or plant disease with the goal of generating fear, causing economic losses, and/or undermining social stability. The goal of agroterrorism is not to kill cows or plants. These are the means to the end of causing economic damage, social unrest, and loss of confidence in government. Human health could be at risk if contaminated food reaches the table or if an animal pathogen is transmissible to humans (zoonotic). While agriculture may not be a terrorist's first choice because it lacks the "shock factor" of more traditional terrorist targets, many analysts consider it a viable secondary target. Agriculture has several characteristics that pose unique vulnerabilities. Farms are geographically disbursed in unsecured environments. Livestock are frequently concentrated in confined locations, and transported or commingled with other herds. Many agricultural diseases can be obtained, handled, and distributed easily. International trade in food products often is tied to disease-free status, which could be jeopardised by an attack. Many veterinarians lack experience with foreign animal diseases that are eradicated domestically but remain endemic in foreign countries. In the past five years, "food defence" has received increasing attention in the counter-terrorism and bioterrorism communities. Laboratory and response capacity are being upgraded to address the reality of agroterrorism, and national response plans now incorporate agroterrorism.