A terrorist who wanted to launch a smallpox attack, however, would probably have a very hard time getting hold of the virus. Smallpox was eradicated in 1980. Officially, only two stores of the virus exist, for research purposes, in secure locations in the U.S. and Russia. There may be covert stashes in Iraq, North Korea and Russia, but these countries would be reluctant to release them, fearing a smallpox epidemic among their own unvaccinated people. Even if a terrorist were successful in obtaining the virus, his plans could backfire: smallpox is so contagious that the first victims are likely to be the members of his own terrorist cell.

Anthrax
Many bacterial agents can be used as bioweapons, including Clostridium botulinum (botulism) and Yersinia pestis (plague). But anthrax stands out because its spores are particularly hardy; they are resistant to sunlight, heat and disinfectant, and can remain active in soil and water for years. Anthrax occurs naturally in both wild and domestic animals‹including cattle, sheep and camels. Infection from direct contact with affected animals is fatal in 20% of cases. If inhaled, however, anthrax spores cause death in almost 90% of the time.

Yet manufacturing sufficient quantities of any bacteria in a stable form is a technical and scientific challenge; plague bugs, for example, degrade within hours when exposed to the sun, and anthrax spores tend to clump together in humid conditions. The Japanese cult Aum Shinrikyo sprayed anthrax and botulism eight times over parts of Tokyo without effect.

Despite all the attention being given crop dusters, using one to spread germs is not as easy as it sounds. The planes are designed to spray pesticides in heavy, concentrated streams, whereas bioweapons are ideally scattered in a fine mist over as large an area as possible. The nozzles in crop dusters are best suited to discharging relatively large particles — 100 microns in diameter — not tiny one-micron specks of bacteria.

Sarin
Unlike biological agents, which are living organisms that require proper conditions to survive, chemical weapons such as the nerve gases sarin and VX are relatively easy to acquire and stockpile. Chemicals are difficult to manufacture in sufficient quantities for a large-scale attack, however; more likely are isolated assaults such as the 1995 sarin attack on a Tokyo subway that injured thousands and killed 12.