"The Alibekov anthrax became fully operational in 1989. It is an amber-gray powder, finer than bath talc, with smooth, creamy particles that tend to fly apart and vanish in the air, becoming invisible and drifting for miles. The Alibekov anthrax is four times more efficient than the standard product.
...
When I assured him I wouldn't, he told me the formula for the Alibekov anthrax. He uttered just one sentence. The Alibekov anthrax is simple, and the formula is somewhat surprising, not quite what you'd expect. Two unrelated materials are mixed with pure powdered anthrax spores."
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http://cryptome.org/bioweap.htm But Rip is right, smallpox is the dinger. A smallpox outbreak would cause massive disruption to our way of life, since:
A. It is HIGHLY contagious, airborne, bloodborne.
B. Hardly anyone in the US is vaccinated.
C. There's not enough vaccine on hand to handle a decent-sized epidemic.
http://cryptome.org/smallpox-wmd.htm There's also a really good story linked at the top of that page describing the dangers.
Spitboy -SW-