Have you ever used a neighbors WiFi connection?  It's considered stealing, much like if you would run an extension cord and plugged into one of their outlets.  If you put it that way, no one would steal a WiFi connection.  If you have a wireless router, you need to put a password protect on it now.  You computer has an IP address for several reasons.  One of them is so that if you are doing something illegal, authorities can get you.  This is the primary way that authorities combat child pornography and sex offenders.  A story I read really brings this to light.  If your child pornographer neighbor is stealing your internet, the law will be coming to your door.

Lying on his family room floor with assault weapons trained on him, shouts of “pedophile!” and “pornographer!” stinging like his fresh cuts and bruises, the Buffalo home­owner didn’t need long to figure out the reason for the early morning wake-up call from a swarm of federal agents.

That new wireless router. He’d gotten fed up trying to set a password. Someone must have used his Internet connection, he thought.

Definitely set a password on it so you don't have to go through this embarrassment.