Scientists have been sending signals to the extraterrestrial – ignoring Stephen Hawking's warning that trying to entice extraterrestrial life to Earth may not be the smartest idea.

And if there was any more reason to be cautious when trying to get in touch with other worldly beings, the PhD student Alberto Caballero has revealed just how many other civilisations we could be antagonising, reminding scientists that 'zero risk does not exist' when trying to contact aliens.

Caballero, who studies conflict resolution at the University of Vigo in Spain, said it has become 'urgent to find an approximation to determine how likely it would be that an intelligent civilisation living in the exoplanet we message has malicious intentions and poses a threat to humanity'.

In the paper, titled 'Estimating the prevalence of malicious extraterrestrial civilisations', Caballero wrote: "Zero risk does not exist, and will never exist. However, if such risk is similar than that of other natural catastrophic events that could affect the entire Earth, then the advantages that would derive from finding and communicating with an intelligent civilisation could greatly exceed its drawbacks.

"Ironically, this would be the case if the extraterrestrial civilisation is far more advanced than ours, which could allow us to improve our technology and provide humanity with significant benefits.

The Milky Way most likely has four alien civilisations which might be malicious and can end up invading the Earth owing to the practice of METI. This statement is not ours but of Alberto Caballero, a Ph.D. student in conflict resolution at the University of Vigo in Spain who claims to have pinpointed the source of the WOW! signal. But before we understand what that signal is, it is important to know what is METI. Short for Messaging Extra-terrestrial Intelligence, METI is the practice wherein astronomers send encoded messages into outer space for aliens to find them and respond.

What was the WOW! signal?

A few decades ago, the Ohio State University-based Big Ear telescope received a powerful burst of radio waves that turned out to contain an alphanumeric code. Having emerged in 1977, the signal lasted 72 seconds and was a big surprise for astronomers. The signal soon became of great interest of research and is considered the best candidate signal under the six-decades-old Search for Extra-Terrestrial Intelligence (SETI) program.

In order to make an estimation, Caballero – who found a possible source behind the Wow! Signal – looked at the 'frequency distribution of the countries that have invaded others between 1915 and 2022'.

During that time period, the researcher discovered that a sum of 51 countries had invaded another.

He then assessed the possibility of each country being invaded by weighing each country up against 'its percentage of global military expenditure'.

"With a weighted average mean, the individual probabilities of invasion are then added and divided by the total number of countries in order to estimate the current human probability of invasion of an extraterrestrial civilisation," he continued.

Looking at energy consumption, average rates of global invasion, the estimated number of intelligent civilisations within the galaxy and the probability of one having 'malicious intentions', Caballero resolved there is an 'estimated probability of 5.52E-8 per cent that a seven messaged extraterrestrial civilisation – or a faction of it – would have hostile intentions towards humanity, as well as a total of 0.22 malicious civilisations'.

According to reports, this finding equals four potentially 'malicious' extraterrestrial civilisations.

Interestingly, Caballero claimed to have located the exact source of the signal, which is from a Sun-like star lying about 1,800 light-years away from Earth in the Sagittarius constellation.

There are four destructive civilisations out there: Caballero

Due to how much of a 'secret topic' attempting to communicate with aliens is, and the fact there's 'very little research on whether it's actually dangerous to do', Caballero suggested the next step should be an 'international debate to determine the conditions under which the first serious interstellar radio or laser message will be sent to a nearby potentially habitable exoplanet'.

He concluded: "It is necessary to mention that the probabilities are cumulative, which means that sending radio messages to several potentially habitable planets raises the total to the sum of all of them, which is in any case an extremely low probability.

"We could send up to 18,000 interstellar messages to different exoplanets and the probability of invasion by a malicious civilisation would be the same as that of an Earth collision with a global-catastrophe asteroid."

The conflict resolution student estimates that there are four major "malicious extraterrestrial civilizations" hidden somewhere in the Milky Way galaxy. According to a report by Vice, Caballero revealed that he made these assumptions based on the calculations done on the number of external “invasions" that occurred on Earth in the last 50 years. He then applied the data to the number of known and potentially habitable exoplanets with Italian SETI scientist Claudio Maccone's estimate of the number of possible civilisations as a reference point. Maccone had made a wild claim that there are as many as 15,785 civilizations in our galaxy.

It is worth noting, however, that Caballero's study is not peer-reviewed and it also admits that the probability of Earth being invaded by aliens is very, very low. For scale, it is two orders of magnitude lower than a planet-killing asteroid colliding with Earth. Besides, He himself admitted that his study has limitations but added that his work would open doors for conditions to send a radio message to the next habitable exoplanet.