IP adresses are only easy to spoof if you do not intend to receive any ACK packages (or any other reply from the target, like web pages with phone numbers on th

IP adresses are only easy to spoof if you do not intend to receive any ACK packages (or any other reply from the target, like web pages with phone numbers on them). For everything else you need the cooperation of a rogue ISP on the shortest path between the target and the legitimate owner of the address block, or a peering with well connected networks that allows you to mess with BGP, which would be hard to hide and probably cost you your peering agreements.