Not sure how this could even theoretically work. Without having a partial understanding of the intended recipient, a radio signal can't cause harm. Something like 'this signal is false' and 'divide by 0' need to be decoded and processed before they are malicious. Meat space is excellent at detecting and breaking these logic problems and infinite loops. We're safe from evil alien signals. Perhaps a decompression bomb within the signal could cause lots of decoding grief. Now that I think about it, I can imagine us being stupid enough to dedicate all our resources into decompressing or cracking an alien signal to up to the point of extinction. And maybe that's when they step in and call it. We were just part of a great galactic prank.