A civilization of machines would not be constained by Sagan’s hypothesis. They could infect our machines to destroy us, in effect turning earth technology into Decepticons.
The. Best solution if we find signals from apparently hostile aliens would be turn earth into “foretress earth” which would involve moving all life on earth underground while nuking the surface repeatedly and sending out fake news signals documenting a “world wide themonuclear war” then sucking all the air off the surface and leaving earth to be a “lifeless” rock and hoping the mothership finds mars a nicer place to pillage....