Pedro Martínez: It could be a family member. Two computers connected to the internet would most likely connect through a router. Once the connection goes out on the internet, they would both have the same IP address. What would be a better tracking would be their MAC address. This is used for NAT so that data comming back can find the appropriate computer. Remember, to the internet, everycomputer behind a router appears to have the router's IP address.

Did I get this right?