Indeed, a better plot would be to use social engineering to let us build the virus/whatever for them: they send us instructions on how to create some beautiful

Indeed, a better plot would be to use social engineering to let us build the virus/whatever for them: they send us instructions on how to create some beautiful technology (e.g. a fake superluminar com) which is so obscure and intricate that it hides his real goal: a sophisticated AI which would then study us and plan for next move <put here your evil plan of choice>. (Variation on the theme of A for Andromeda)