SEATTLE -- We have a warning about a popular way to surf the Internet at home.

You're about to see just how vulnerable wireless networks are to hackers.

Security experts show us how they can spot credit card numbers -- and even crack passwords.

Wireless networks let you move around with a laptop and surf the Web from anywhere at home.

Surveys show nearly half of all home broadband users now connect by Wi-Fi.

We discovered how easy it is for hackers to tap into your network and watch everything you do online.

We drove through Federal Way with computer science student Dan Gamble.

"In that short drive we've picked up an additional 30 networks," he said.

Each green dot on his laptop is a Wi-Fi connection in a home or business.

"We have 45 sitting right here," he said.

Many of the networks don’t have a padlock icon.

"I'd say one in four is unencrypted," Gamble said.

That means the owner never set up basic security protections.

Using readily-available software, Gamble can spot who simply pulled the hardware out of the box.

"They plugged in their router. They said, 'All right, we have wireless. We're good.'"

But there are dangers. Without encryption, anyone can borrow your connection.

Worse, there's nothing to slow down a hacker from tracking your activity online -- and stealing your identity.

"There are malicious people out there. They will take advantage of your Internet connection," Gamble said.

There are two kinds of Wi-Fi encryptions: WEP and WPA.

But even they can be cracked.

Damon Cortesi and Walter Pearce showed us how.

At the security company Ioactive, they're professional “hackers.”

"Yes, but the good kind," Cortesi said. "We're there to help and protect."

They had me put in a password as if I were setting up a home network with WEP encryption.

I chose "Molly" -- the name of my dog.

"You set it. We don't know what it is," Pearce said.

With software easily found online, Pearce ran a statistical analysis.

Twelve minutes later:

Pearce: "There we go."
Johnson: "Those numbers are the name of my basset hound?"

In computer language, "Molly" is actually this: 9ec73e76.

With this code, Pearce spied on my Wi-Fi connection. Cortesi -- logged in as me -- went shopping.

Pearce showed us how he can spot log-ins and credit card numbers.

Just imagine what he'd see if Cortesi was filing his taxes.

It took even less time to crack the password for a WPA encryption, which is considered more secure.

"This software will try to guess passwords at hundreds of passwords a second at the very minimum," Cortesi said.

The program simply found the password in a dictionary.

So, with Wi-Fi encryptions, this easy to crack. What should you do?

The key is how you pick your password.

Use something that's definitely complex. If it uses special characters, that's even better.

Here's the idea: Instead of typing "molly," use a sentence. The longer your password -- the harder it is to crack.

A combination of upper and lower case letters also helps.

You can bet something like "mOllYbASsETisthe#1Drooler" won't be in any dictionary.

This will be harder to remember, but Windows will save your password so you don't have to retype it every time.