It’s the basic level of Internet access — the residential wireless network. And often it’s the least secure, guarded by simple passwords or none at all.

The recent case of a Kalispell couple whose network was used to download illegal material has shown what can happen when somebody gains access to an Internet network with bad intentions.

According to experts in Internet security, it happens more often than one might think.

“I would bet you right now that 50 percent of the routers in this state are being used by someone that is not authorized,” said Scott Thompson, a Bozeman-based computer network expert and consultant. “And I think that’s probably a conservative number.”

Most of those aren’t malicious intrusions, he added. It could just be somebody looking for free Internet access, but it leaves the network open to trouble.

It isn’t the most complex form of cyber-crime, with massive hacking schemes and international espionage. Somebody gains access to another person’s Wi-Fi network and commits crimes under the mask of the owner’s Internet Protocol address — the numerical code that identifies a specific Internet device.

Often, a residential Internet subscriber will be assigned a single public IP address. So if anybody commits a crime on that Wi-Fi network, it could be traced back to the subscriber’s IP. Like identity theft, a crime would be committed under the owner’s name.

That’s what happened to Rodney and Margaret Stell of Kalispell. They had no idea someone had gained access to their Wi-Fi until armed federal agents showed up at their house with a search warrant.

The Department of Homeland Security had traced child pornography to the IP address owned by Rodney Stell. Homeland Security later confirmed Stell was innocent and his network likely had been hacked.

A spokesman for Homeland Security said that this is a situation that happens “a lot.” Criminals get access to an innocent person’s network and do harm.

The best defense is a user-level offense.

“This is a situation where people should definitely secure their wireless router to ensure that nobody else steals their Internet,” and consequently results in them becoming “a victim of a search warrant that they had nothing to do with,” said Carl Rusnok of Homeland Security.

Johnson agreed that it starts with the Wi-Fi owner. He has worked in the computer business since 1984. For the past 15 years, he has specialized in wireless networks. That includes working with manufacturers, writing protocols and consulting private businesses.

Johnson deals with network intrusion cases weekly. He was tapped by Stell’s attorney following the search warrant to establish that someone other than the registered owner could easily be working behind an IP address.

“Dependent upon the resources there and who installed them and how they’re configured, it could be as easy as sitting in a car two miles away and using them — or it could be more difficult,” Johnson said.

The simple way into someone’s Wi-Fi is knowing the password. The more difficult route is through software that’s intended to break through a password encryption. Johnson called them “brute force attack” programs.

He said that in many cases, people don’t want to deal with all the security features of their wireless router and put a simple password in place.

Those are the most vulnerable to password-cracking programs.

It might take a few days for that software to crack a password with 10 characters. Johnson suggested something a bit more robust.

“If you make the wireless password 20 to 30 characters, which almost nobody wants to do, it would take two or three years to break it,” he said.

The other part of consumer-level protection is to have modern equipment, he said.

What may have been secure in 2006 could be easily cracked in 2015. A router that has WPA2 encryption is the best choice for most users.

Johnson suggested that this could end up becoming a larger problem with public Wi-Fi access. Using another IP address, he said, can be a mask for individual users.

As in the Stells’ case, whatever happens on a Wi-Fi network is traced back to the IP owner.

“Treat it with the value it deserves,” Johnson said. “You’ve got to realize that that is your address. It’s like your gun, right? You point it and pull the trigger, [and] they’re going to trace it back to you. And lots of people just don’t treat it that way.”

Reporter Matt Hudson may be reached at 758-4459 or by email at mhudson@dailyinterlake.com.