Obscurity doesn't mean undetectable. Also: you would still need to do a more elaborate (and therefore more "expensive") full range port scan, compared to scann

Obscurity doesn't mean undetectable. Also: you would still need to do a more elaborate (and therefore more "expensive") full range port scan, compared to scanning just the standard ports. That doesn't scale so well for scanning many IP address (e.g. criminals scanning the internet for potential targets).