The supposed authors (who claimed to be extraterrestrials) of a set of mysterious letters sent from all over the world to a particular group of Spanish and French scientists. These letters were filled with rather prophetic scientific concepts.

They are also supposedly connected with a UFO sighting in Voronezh, in the former Soviet Union. The symbol that they use in their letters looks something like this: )+(

It is also equally possible that this is a complete hoax, created by a Spanish psychologist, Jose Luis Jordan Pena, who said that he wished to demonstrate that paranoia is more widespread than we realize.