Two astrophysicists warn that passive SETI could be dangerous [seti.org] due to malicious code, blueprints, or ultimatums sent to Earth by aliens or alien AIs:
With all the news stories these days about computer hacking, it probably comes as no surprise that someone is worried about hackers from outer space. Yes, there are now scientists who fret that space aliens might send messages that worm their way into human society — not to steal our passwords but to bring down our culture.
How exactly would they do that? Astrophysicists Michael Hippke and John Learned argue in a recent paper [arxiv.org] that our telescopes might pick up hazardous messages sent our way — a virus that shuts down our computers [nbcnews.com], for example, or something a bit like cosmic blackmail: "Do this for us, or we'll make your sun go supernova and destroy Earth [nbcnews.com]." Or perhaps the cosmic hackers could trick us into building self-replicating nanobots, and then arrange for them to be let loose to chew up our planet or its inhabitants.
But don't worry? [vice.com]
Although it may be rational for us to engage trade with this alien AI, the researchers ponder the consequences if the cure for cancer involves, say, building an army of nanobots from blueprints provided by the AI. In a sort of reverse-Contact scenario, the researchers imagine a scenario in which the machine blueprints turn out to be malicious. Perhaps humans build these cancer-curing nanobots and they are actually programmed to deplete Earth of certain vital resources.
The scenarios offered by the researchers are pretty far out, but are worth taking seriously in the event we ever establish contact with an extraterrestrial intelligence. Still, that's not necessarily a reason to refrain from opening the message. "Our main argument is that a message from ETI cannot be decontaminated with certainty," Hippke and Learned conclude in their paper. "Overall, we believe that the risk is very small (but not zero), and the potential benefit very large, so that we strongly encourage to read an incoming message."