Invisible foot soldiers.

Biological warfare, the use of agents such as bacteria and viruses, is also covered by international law. While chemical weapons are seen as the equivalent of nuclear bombs for poor countries, biological weapons are described as the foot soldiers of the 21st century.

According to Dr. Graham Pearson, head of Britain's chemical and biological defence unit, they are cheaper and easier for small countries to obtain than atomic weapons. "Anthrax, sprayed from the back of an aircraft on a cool, calm night, could take out all of Washington, D.C. This could cause up to three million fatalities, compared to two million from a hydrogen bomb."

U.S. intelligence agencies claim 10 countries are involved in prohibited biological weapons research.

In 1972, the U.S., the former Soviet Union, and more than 100 other countries including Canada, signed the Biological Weapons Convention which bans the development, use, and stockpiling of biological weapons. The agreement essentially outlawed biological warfare but it didn't prohibit defensive research. Nor did it include provisions to verify compliance.