Network Registry links
All communications on the Internet have a source and destination address, this much is obvious. But, there it easy to spoof (or falsify) the source address of network traffic, making it easy for an hacker to hide while attacking a target.
Spoofing doesn't always work, because a hacker can't have a conversation with a victim system using spoofed packets. At some point, the hacker will need to use a legitimate IP addresss. Then, we can use network registry and ownership authorities to determine the who behind an IP address.
Information on how addresses are allocated.