Aliens coming to planet Earth for a quick chat and visit would probably top any other global headline news that day.
But what if they weren't the ET-amiable type and more the blow-us-up Independence Day kind?
One PhD student in Spain has considered such scenario and calculated that approximately four "malicious extra-terrestrial civilisations” could be living in our very own Milky Way right now.
However, Alberto Caballero's paper called Estimating the Prevalence of Malicious Extraterrestrial Civilizations - which has not been peer reviewed - concluded that the chance of an evil alien race invading Earth is "very low" and that we are more likely to be killed off by a giant asteroid.
Caballero, who studies conflict resolution at the University of Vigo, admitted that there were limitations to his thought experiment - for example not understanding how an alien mind might work.
He told Vice : "I did the paper based only on life as we know it. We don’t know the mind of extra-terrestrials.
"An extra-terrestrial civilisation may have a brain with a different chemical composition and they might not have our empathy or they might have more psychopathological behaviours."
The student used a series of mathematical equations to arrive at this theory.
He first estimated the likelihood of different nations on Earth invading each other, which he used to work out the chance of Earth as a whole attacking another planet.
Once the human race has mastered interstellar travel - in 259 years, according to the paper - then there is a 0.0014% possibility of us invading aliens.
From there he believes there could be 4.42 hostile civilisations in the Milky Way that could also be like humans and attack us once they know how to space travel.
But, he added: "I don't mention the 4.42 civilisations in my paper because 1) we don't know whether all the civilisations in the galaxy are like us… and 2) a civilisation like us would probably not pose a threat to another one since we don't have the technology to travel to their planet."
In his calculations he also used a 2012 paper published by space scientist Claudio Maccone on the search for alien life that estimated there are a theoretical 15,785 alien civilisations living in our galaxy.
Caballero is also the author of another study that was published this year in the peer-reviewed International Journal of Astrobiology.
In it he attempted to find the origin of the Wow! Signal, a radio signal detected in 1977 that some believe was a made by aliens.
