smallpox found!!
Although it was eradicated in 1979, it has been found on some 50 year-old tissue samples in Russia and at the CDC headquarters in Atlanta, Georgia. But it is feared that there may be unregistered reference samples in other countries that have not admitted to having it yet that may use it in chemical warfare against us or our allies.
I think that if we are careful and keep ourselves immunized against it, then we will be just fine, as long as nobody decides to get smart and genetically engineer it so that it is automatically resistant to any known vaccine for the original strain. If you want more info, go to this site