Ken Alibek describes (in Biohazard) some of the basics of the Soviet bioweapons program:
At the height of the U.S. offensive biological weapons program, American scientists restricted themselves to developing armaments that could be countered by antibiotics or vaccines, out of a concern for protecting troops and civilians from potential accidents. The Soviet government decided that the best agents were those for which there was no known cure.
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Trafficking in germs and viruses was legal then, as it is today. In the name of scientific research, our agents purchased strains from university research laboratories and biotech firms around the world with no difficulty.
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It was from the United States, for instance, that we obtained Machupo, the virus that causes Bolivian hemorrhagic fever. We picked up Marburg, related to the Ebola virus, from Germany.
The KGB was our most dependable supplier of raw material. They were known within Biopreparat by the code name “Capturing Agency One.” Vials arrived in Russia almost every month with exotic fluids, powders, and cultures gathered by our intelligence agents in every corner of the globe. They were then sent by diplomatic pouch to Moscow, where Biopreparat technicians cautiously repackaged them.
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We were never permitted to travel by air. The consequences of a crash in one of our aging Aeroflot planes was too horrible to contemplate. Instead, dressed in civilian clothes, we returned in the cramped, sweaty passenger compartments of trains, trying to be inconspicuous.
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We even explored AIDS and Legionnaire’s disease. Both, as it happened, proved too unstable for use on the battlefield or against civilian populations.
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One of the most infectious diseases known to man, smallpox, was declared eradicated by the World Health Organization in 1980. The last naturally occurring case was reported in 1977, and the medical profession judges the minor health risk associated with a vaccine greater than forgoing inoculation. Today, it isn’t possible to get a smallpox vaccination in the United States, unless you are a lab scientist or a member of the military. This was for us an excellent reason to weaponize it.
Although we officially had a small amount of the virus in the Ivanovsky Institute of Virology in Moscow—matching the world’s only other legal repository of the strain in the United States—we cultivated tons of smallpox in our secret lab in Zagorsk (now Sergiyev Posad), the famous Russian cathedral city a half hour’s drive from the capital. At Zagorsk, we experimented with the culture until we came up with a weapons-quality variant. Smallpox was then quietly added to our arsenal.