One of the big-sellers this holiday season is the wireless router, which lets you link your computer to the Internet from any room in the house.
But as CBS News Correspondent Vince Gonzales reports, the problem is that strangers on the street can also hook up to the net -- through your router.
It's called "war-driving" -- prowling neighborhoods, searching for open wireless networks that offer a free ride onto the Internet.
Frank Keeney is a computer security consultant. He and CBS' Vince Gonazales went driving, to the accompaniment of "boing, boing, boing."
"What does it mean every time it beeps like that,'' Gonzales asked.
"Well every one of those beeps represents a wireless router that someone has installed in their home or their business,'' said Keeney.
Gonzales: "It looks like a fair number of them are not running a security program."
Keeney: "That's right."
Most consumers skip a key step when setting up their wireless systems -- activating built-in security programs to keep others off their network.
Those signals don't stop at your property line and can be picked up some distance away -- as we found out when Keeney accessed our system.
"I'm on the Internet right now, and it's through the antenna on my car,'' said Keeney.
He had our permission, but ….
"There is also the possibility of people doing other malicious things like sending spam, downloading illegal material or other information that might be tracked back to you instead of the person using it,'' said Keeney.
In fact, one man was arrested last year driving through Toronto using wireless systems belonging to unsuspecting home-owners to download child pornography.
"This is the crime of the future,'' saus Wes Hsu, an Assistant U.S. Attorney in Los Angeles.
In Los Angeles, the Justice Department recently obtained the nation's first guilty plea for "war spamming."
"He found an unprotected wireless router and then used that laptop that was sitting in his car to send out adult pornography spam,'' said Hsu.
Keeney says with the right programs, trespassers can also track your e-mail and the Web sites you visit. They can steal passwords and credit card numbers, and look through your files.
But a few easy steps that turn on security programs are the best way to protect against drive-by hackers.