The case of the stolen Wi-Fi: What you need to know

Benjamin Smith III and Gregory Straszkiewicz both were arrested for allegedly stealing something no one could see, hear or feel. That thing was valuable enough for victims to press charges in both cases. But the arrests were over something many consumers throw out their windows every day: a Wi-Fi signal.

The idea of a police car roaring down the street to catch a roving "Doom" junkie using someone else's wireless LAN may seem silly, but there are real dangers if your network plays host to strangers. The hazards you might face include eavesdropping, theft of data, painful legal hassles or even a conviction for computer-related crimes. And if you casually tap into your neighbor's Wi-Fi sometimes, these arrests -- Smith's in Florida and Straszkiewicz's in Isleworth, U.K. -- signal that it's at least possible you might run afoul of a law and an irritated fellow citizen.

On April 21, Richard Dinon of St. Petersburg, Florida, called police after he saw Smith in a car on the street outside his house using a notebook computer. Smith, 40, was arrested and charged with a felony under a Florida law that prohibits unauthorized access to a computer or network, according to police. A pretrial hearing is set for Sept. 8. In July, a court in Isleworth convicted Straszkiewicz of using a laptop to access the Internet over unprotected residential wireless LANs on several occasions. He was fined 500 pounds (US$874 at the time) and got a 12-month conditional discharge.

A typical home Wi-Fi signal can transmit about 150 feet (46 meters) from an access point or router. Walls and windows will slow it down, but if it reaches the edge of your property, it won't stop there. In densely populated areas, it's common for a Wi-Fi device such as a notebook to detect multiple residential networks from one place.

It's not hard for even an innocent user to tap into a broadband Internet connection via an unprotected wireless LAN: As soon as the Wi-Fi client detects the network, the user can click on it and join. Some broadband subscribers even like opening their networks. But Internet access may not be the only thing being shared.

"People who steal bandwidth aren't necessarily going to stop there; they might steal data as well," said Gartner Inc. analyst Richard Hunter. Most consumers wouldn't even know if a stranger was using the network, he added.

"If you've got an unprotected Wi-Fi network and you are in any kind of populated area, then you really should do something to protect that," Hunter said.

Specifically, on a Windows PC, a intruder on your wireless LAN could get into any folder that is set with file sharing enabled, Hunter said. Whatever is in the file could be modified, copied or posted on the Internet. So whatever you do, file sharing should be disabled, or restricted to certain trusted people on every folder, he said. That would at least prevent "a very casual hacker" from snooping in your files, Hunter said. File sharing is enabled by default in Windows XP Home Edition, according to Microsoft.