Scientists at the Australian National University in Canberra made the original discovery by accident, though their virus only killed off sixty percent of infected mice. As a side effect of introducing IL-4 into pox viruses, the virus becomes species specific and non-communicable, though no one is quite sure why this is the case.
The implications of this discovery and their disclosure are staggering. IL-4 is a protein common in genetic research and as such is available on the Internet for as low as sixty dollars. Furthermore the procedure is simple, something that a biology graduate student should be able to manage without trouble. The bio-terrorist potential for an IL-4 modified pox virus that infects humans is extraordinary. Like anthrax, only those who come into contact with the virus itself would become infected. The virus would not spread and infect the attackers. Neither would it require state of the art scientific facilities to create such a virus. Buller and his team are currently working on a drug to resist the new viruses, but have so far been unsuccessful in making it 100% effective.
http://www.projectcensored.org/publications/2005/15.html