It is common for hosts for a domain to have completely different IP addresses. Scanning the IP range that a domain belongs to has very very little value. That script may find domains that don't even belong to the same owner, AND... miss other domains that DO belong to the same owner. If you enter "secure.net" into that PHP script, you'll see what I mean.
I mention this so that people don't get there hopes up.
It's just a glorified scan.