I guess

The program of the search of extraterrestrial intelligence (SETI) is a source of extinction risk. The main idea is that passive SETI is much more dangerous activity than messaging to stars because we could download Alien AI (that is a scheme of a computer and program to it) which will use the Earth to send its copies further. The following is based on two premises:
First is that extraterrestrial civilizations do exist in the distances which allow radio communication, but do not allow interstellar travel (which is from one thousand to one million light years).
Second is that artificial intelligence is possible as a self-evolving classic computer program.