Scientists now fear the human race faces the danger of being hacked...by aliens. In a new paper, astrophysicists Michael Hippke and John Learned argue that aliens may seek to destroy our civilization but not with the extravagant and bellicose weaponry seen in Hollywood films like Independence Day. Rather, we may contract hazardous messages through our telescopes, such as a virus that shuts down our computers. Or they could even extort us, making us mine a precious mineral or asteroid for them. “Do this for us, or we’ll make your sun go supernova and destroy Earth.”
It's possible they could release some code that completely disrupts our computer systems, or even trick us into creating some form of technology that destroys us, such as nanobots.
The point is if aliens wanted to hurt us, they could probably do so without ever even having to come here.
I, personally, think this is unlikely. An extraterrestrial race that is significantly advanced enough that they have mastered interstellar transmissions or travel would probably be operating on a different wavelength than us. It's possible they are post-biological and exist as some extraterrestrial form of artificial intelligence; or maybe they are forms of pure energy, such as the entities seen in 2001.