Editor's note: Conscious of the controversial nature of this article, Technology Review asked Allison Macfarlane, a research associate in the Science, Technology, and Global Security Working Group in MIT's Program in Science, Technology, and Society, to rebut its argument: see "Assessing the Threat." We were also careful to elide any recipes for developing a biological weapon. Such details as do appear have been published before, mainly in scientific journals.

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