Last Updated Oct 16, 2017 8:38 AM EDT
The FBI is out with a new warning about an increase in. That's when criminals lie about taking a loved one, and then demand money.
The FBI is launching an awareness campaign on Monday to fight the growing scam.
CBS News has reported on people around the country who gettelling them to send them money, or else. Now, the FBI is investigating at least one of the groups doing it and wants to know who else may have fallen victim to the scam.
CBS News correspondent Anna Werner reports the kidnapping calls came to a father in the Dallas area.
"He told me if I dropped this call, that he was gonna kill my son," Don Ferguson said.
And in the Boston area, a mother of a young woman claims scammers said, "I have your daughter, she's in the back of my van, and I am going to kill her."
Kidnappers called Valerie Sobel in Los Angeles too, saying they'd taken her daughter.
"The man says, 'We have cut off her finger and if you want the rest of her in a body bag, it's your choice,'" Sobel said.
To get her back, he told Sobel she'd have to send them money. And in the meantime, "if you disconnect this phone, she's dead. If you don't follow exactly what I tell you, she's dead," the kidnappers said.
Sobel stayed on the line for over two hours and sent close to $4,000 dollars to Mexico as directed. Then the would-be kidnappers hung up. But her daughter hadn't been kidnapped. She was fine.
The FBI says these fake kidnapping calls are on the rise.
Tim Ferguson is an FBI assistant section chief who says those calls usually come from criminals in Mexican prisons.
"It's a get-rich-quick scheme where they can extort victims and have them wire money into Mexico," Ferguson said.
Ferguson told Werner his department was able to track some of the phones back to prisoners in Mexico. He says prisoners used smuggled cellphones to random-dial numbers in the U.S. and make their threats. Then, prisoners' friends or family pick up the cash sent by victims to money transfer locations.
"I don't necessarily think that it's just in the prison systems, but I would say the large majority of the ones that we do have do come from the prison systems because the individuals there don't have anything but time and they have the resources to do so," he said.
Ferguson says his agents are honing in on one ring of criminals so far, but the FBI is now asking the public to help find others by reporting any fake kidnapping calls they've received.
The agency's goal? To prosecute offenders -- something that did happen in Sobel's case. At least one woman was indicted in federal court on charges, including conspiracy to commit wire fraud.
"They are always learning and they are always adapting and trying to figure out how to make the extortion scheme better," Ferguson said.
So then, how do you know if the call is a fake one? The FBI says out of state area codes are one tip off, or longer foreign numbers.
If there's an urgent demand that you stay on the phone and not get off the phone, that is designed to stop you from contacting your loved one or the police. And the request to wire smaller amounts of money from multiple locations, down to Mexico.
To report a call, you can go to the FBI's website.