I used to worry about that a bit when we discussed this a year or two ago, but then I realized that Earth has been broadcasting the fact that it is inhabited to any civilization only slightly more sophisticated than ours (like, literally only by a couple of years) who can see spectroscopy of our atmosphere when we transit in front of the Sun. Earth has been broadcasting that it has free oxygen for nearly two and a half billion years and we have no evidence of any attack.
I run on the theory that if an alien civilization intended to destroy Earth, they would have succeeded. An alien civilization that reaches out once every few dozen million years years to sorta kinda whack the Earth seems about as likely as aliens hopping in their FTL spaceships and traveling the vast distances across the cosmos to our primitive little dirt ball, only to constantly crash into mountains located near secret military bases.
