BOSTON -- First, there was dial-up Internet service, then came broadband high speed, and now there's wireless, providing access to the Net anywhere at home or on the road.

NewsCenter 5's Jorge Quiroga reported that anyone with a personal computer and a $40 wireless card could get free Internet access at hundreds of airports, hotels and coffee shops.

But, this convenience is not risk free -- millions of computers are targets for digital thieves.

Brian Ford used his pocket PC to browse for unseen treasures in the trendy Newbury Street area.

"Since we walked about 20 feet, I picked up 10 wireless networks," Ford said.

Ford is a wireless security expert. He helps companies find weak spots in their wireless networks and fixes them. But as Ford demonstrated, the same software that lets his PC do safety checks can be used by digital vandals.

Similar to a police radio scanner, the software lets tech savvy vandals hunt through the chatter and catch their prey -- users who have unsecure wireless Internet networks.

"They can access all of your files. They can find out what your credit card numbers are. They can go after your bank balances," wireless expert Jack Davis said.

On Newbury Street in the eight blocks from Arlington Street to Mass Ave, in one hour, Ford picked up 64 wireless networks in use, and 80 percent were unsecure.

"Slowly but surely, you can walk into their world, you know, start taking over bits and pieces of their lives," Ford said.

Like a radio tower, a wireless network's router will broadcast its signal up to 1,300 feet, or the length of a city block.

Some networks require passwords, but others are left open and unsecure for convenience sake. They are called "hot spots" -- like the free network accessible at nearly a dozen Newbury Street restaurants and cafes.

With his permission, Alex Mittsendorf scanned the Web, while Ford cyberpeeked.

"You kind of have that expectation of less privacy in a public place. But at home, you think you are totally safe and secure," Mittsendorf said.

In fact, residential users are even more vulnerable because with less signal chatter it's easier for vandals to target their victims.

"But I didn't realize that people could get into my work and my files," Internet user Joan Weinstein said.

Weinstein didn't know her unsecure home network was being picked by her neighbors. Anyone with a computer and wireless card could piggyback on to her Internet and break into her cyber world.

All of this is easily preventable. Experts say every wireless network sold comes with security features that take just minutes to install.

It's an ounce of prevention that gets you peace of mind for your personal computer.