June 25, 2007  -- Who do you call when your personal cell phone has been turned into a spying device, tracking your family's every move, and giving an anonymous stalker a view into your private life?

Three Washington state families say it happened to them and left them feeling like they were living in a horror movie.

"They say you're going to die, we hate you, we're going to murder you," said Heather Kuykendall, one of the alleged victims. And the families say no one seems to have an answer as to how or why it happened.

The police say they are stumped, but they have not ruled out the possibility that the alleged victims are making the whole thing up.

The families say the calls come in at all hours of the night, threatening to kill their children, their pets and grandparents. Voice mails arrive, playing recordings of their private conversations, including one with a local police detective.

The caller knows, the families said, what they're wearing and what they're doing. And after months of investigating, police seem powerless to stop them.

Cell phone companies are skeptical. "We are unaware of any technology that would allow the activity that's being reported here," said Sprint spokesman Matt Sullivan. "We are partnering with law enforcement to investigate. We're not exactly sure what is being done to these phones."

But, in an age of rapidly advancing technology, some surveillance experts told ABC News it's all too easy for hackers to turn your cell phone against you.

James Atkinson, an electronic surveillance expert, told ABC News cell phones can be operated remotely. "You can take photographs remotely, you can track the person's position, you can figure out where the phone is," said Atkinson. "Most cops have no idea how this is done."

Harassment or a Prank?

The Kuykendall family's troubles started in February when 16-year-old Courtney Kuykendall's cell phone started sending text messages to her friends -- by itself, the family said.

Then the threats came. A scratchy voice called daily, sometimes to say that the entire family's throats would be slit, Courtney's mother, Heather, told ABC News.

But when the Fircrest, Wash., police tried to find the culprit, the calls were traced back to the Kuykendalls' own phones -- even when they were turned off.

It got worse. The Kuykendalls and two other Fircrest families told ABC News that they believe the callers are using their cell phones to spy on them. They say the hackers know their every move: where they are, what they're doing and what they're wearing. The callers have recorded private conversations, the families and police said, including a meeting with a local detective.

Many of the voice mails sound like a teenager's prank. "Sometimes they say real juvenile things. Sometimes it's really scary," Kuykendall said.

In one of the messages, which Kuykendall played for ABC News, the caller said, "I know where you are. I know where you live. I'm going to kill you."

Kuykendall, her sister, Darci Price, and her neighbor, Andrea McKay, who also claim to be victims of similar harassment, have named the callers "Restricted," the name that pops up when the calls come in.

Kuykendall, Price and McKay say their families' phones have turned on by themselves when they were switched off. The ring tones have changed on their own.

The callers seem to know when the kids leave for school and when they are home alone, Kuykendall said. Messages warned the McKays that there would be a shooting at their daughter's school.

The harassment, they said, feels relentless. Kuykendall installed a new security system for the house. Soon after, she got a voice mail from Restricted saying that the callers knew her security code.

Once, McKay said, when she was slicing limes in her kitchen, a call came in from Restricted. The voice said it preferred lemons.

As soon as the Kuykendall family met with police, they say they received warnings not to talk to the cops. Then a voice mail arrived: a recording of the conversation they'd just had with the police.

"The level of fear went from, 'This is a pain,' to an uncontrolled fear and anxiety level," said McKay.

Kuykendall said her family switched phones and opened new accounts twice, but the calls keep coming. "If we go a day without a call, that's a good day," Kuykendall said.

Local Police 'Almost Dumbfounded'

The callers have likely violated several laws, law experts say, possibly including federal wiretapping statutes. But the case has local law enforcement stumped.

"We're almost dumbfounded. We've never seen anything like this," said Fircrest Police Chief John Cheesman, who said he has known the Kuykendalls for years.

Cheesman said he is working with the Tacoma police and the Pierce County Sheriff's Department and has also contacted officials at the department of Homeland Security. But police still are not close to finding the perpetrators.

Most of the harassment appears directed at Courtney Kuykendall, police said, adding that most, but not all, of the calls have been traced back to her phone.

Police are not calling the 16-year-old a suspect, though the unusual tale has raised some eyebrows. "It wouldn't be prudent not to look internally" at the family, said Ed Troyer, a Pierce County Sheriff's Department detective.

"At this point, we aren't saying it's someone inside the family, but it's someone that is close enough to them to know this much about them," Tryer said. "It seems like it's someone who is tied into the group, a family member, a friend or an enemy."

He added, "I hope it isn't coming from within the family because it would be a waste of everyone's time."

" Heather Kuykendall is adamant that her daughter is not involved and said the calls kept coming even when they took Courtney's phone away. She said Courtney was too upset to speak to ABC News.

"We know it's not her," Kuykendall said of Courtney. "And we can't think of anybody we've made mad or if we've made any enemies."

Cyber-Bullying

The calls appear to be just the latest incarnation of so-called cyber-bullying. According to an April 2007 survey of middle school kids by online safety group WiredSafety.org, the most prevalent threat children face through new technology is not the 40-year-old pedophile, but the kid sitting next to them in math class.

At least 85 percent of the middle schoolers polled said they have been cyber-bullied in the last year -- picked on by another child, often anonymously, through the Web or a cell phone.

"These situations recount how kids are hurting other kids -- taking the bullying off of the playground and into a much more anonymous, and often more painful encounter on the phone and online," said Parry Aftab, WiredSafety's director and a well-known Internet security and cyber-crime lawyer.

Cell Phone Manipulation

ABC News spoke with security experts who say they think they have the answer to the Kuykendall's mystery.

It's relatively easy to "spoof" a phone, allowing a person to mask or alter the number he or she is calling from, said ABC News consultant Brad Garrett, a former FBI agent. More sophisticated hackers can also clone a cell phone, allowing them to do just about anything the victim could do with the original phone, Garrett said. But cloning a phone would not allow someone to listen in on a phone call, which requires more sophisticated technology, Garrett said.

Atkinson, a communications engineer who recently testified in front of Congress about a leak of classified Coast Guard information, told ABC News this case sounds like a game of "cell phone manipulation."

Atkinson, who said he has been trained by the National Security Agency, said the perpetrators would probably have to hack into a Web site operated by the cell phone companies.

"Someone is manipulating the software and firmware in their cell phones and are exploiting weaknesses or 'features' in the phone, like the GPS, customized rings, and internal voice mail, that are installed by the manufacturer to provide special services," he said. Despite the complexity of the software programs used to hack into phones, technology experts say that even a prankster new to the game can cause trouble.

Inexperienced hackers, often called "script kiddies," can use programs developed by more tech-savvy hackers to break into computers and cell phones, Atkinson said. Commonly between the age of 15 and 25, script kiddies see these hacks as a way of asserting themselves, he added, much in the same way bullies beat others up.

Countless technology companies have contacted the McKays this past month, claiming that they have the equipment that police lack to find the hackers.

Detective Troyer disagreed. "We have that technology, and yet all of our tracking leads to dead ends," he said.

Destined for Pay Phones?

Before you swear off cell phones forever, Garrett told ABC News there are some simple ways you can protect yourself from cell phone harassment.

Do not disable the password on your phone and change your password regularly, he said.

You can also purchase wireless security software online, which will make it more difficult for a hacker to spoof your phone.

If your phone has already been hacked, take it to the police. Then get a new phone and a new account and "do not give the new numbers away to a living soul" warned Atkinson.

Tell the cell phone provider to make note in the account that you've had problems with a hacker in the past, which would throw up a red flag if anyone claims they are you when speaking to the cell phone company.

"This should educate people about the pitfalls and the lack of privacy we all have if someone wants to put the energy into it," Garrett said.