[Lingering Haze]

It is clear that the program must not be checking through the ISP for a name because ISPs do not retain that kind of information in a public file.

It has to be checking somewhere that the computer user has entered their name. If someone has named their computer on the domain using their name, then that might be one possible way to find it. Also, if they have entered their name when they registered windows you might be able to pull the information from there.

However, I think most firewalls protect against sending out that kind of information. Most computers have some form of firewall protection nowadays, so you probably will not be able to find out their last name simply by using their IP.

If you really wanted it badly, you could go to the local ISP branch that runs their service and ask for the last name. They probably won't just give it to you, so you would have to pretend you are some official or find some way to trick them.