The phrase "alien attack" refers to a situation where beings from other planets come to harm or invade Earth. It suggests the existence of extraterrestrial life that is hostile towards humanity and poses a threat to our planet. Full definition
Go to war, shoot opponents, kill zombies, and defend against alien attacks! (poki.com)
Since the first alien attack, the alien technology has been used to supposedly build up the world's defenses against another attack. (businessinsider.com)