DIANE SAWYER (ABC NEWS)(OC): And now a scam sweeping the country, 25,000 complaints, cheating people out of $100 million just last year alone. Thieves who can imitate the voices of your children, your friends, your grandchildren and trick you into sending them emergency money. ABC News's Ron Claiborne shows us the clever way they do it.
RON CLAIBORNE : They are the sweetest of victims of the cruelest of scams, one that preys on the love of a grandma or grandpa for unscrupulous profit.
ANN WARREN (GRANDPARENT): And he said they want $2,400, grandma. I know it's an awful lot of money, but can you please, please.
RON CLAIBORNE : Ann Warren was sure it was her grandson Matthew on the phone from Barcelona, with a story of woe that included a car crash, a jailhouse stay and demands for restitution by Spanish police.
ANN WARREN : I was determined to help my grandson.
RON CLAIBORNE (ABC NEWS)(VO): Tricked by the voice on the end of the line, she wired the money, twice. How do these scammers do it?
RON CLAIBORNE (ABC NEWS)(VO): TMI, too much information posted online. Using sites like Facebook, they pull together convincing information, photos, so they can ask about your dog, Daisy or your new car. And most useful of all, they can hear their voice in the posted video and know even what they sound like.
POSTED VIDEO (FEMALE): Who's texting you? Who's texting you? Who's calling?
RON CLAIBORNE (ABC NEWS)(VO): I've known my cousin James all his life and I would do anything if he or his family needed help. So I asked him to record a fictitious plea just like the ones those scammers do.
JAMES (COUSIN): Hey, Ron. This is your cousin James. I'm sorry for the bad connection but I really need your help. I'm in a lot of trouble.
JAMES (FAKE COUSIN): Hey, Ron. This is your cousin James.
RON CLAIBORNE : Then had someone else study his voice to see if they could mimic him convincingly.
JAMES (FAKE COUSIN): Hey, Ron. This is your cousin James. Sorry for the bad connection, but I really need your help. I'm in a lot of trouble.
RON CLAIBORNE : If I were concerned, I probably wouldn't notice the difference, which makes it truly admirable that this grandma finally became a kind of Sherlock Holmes. On the third call, the thieves made a key mistake.
ANN WARREN (GRANDPARENT): And that's when he called himself Matt, not Matthew.
RON CLAIBORNE : A nickname her grandson never uses. Ann called her son, who said that Matthew was at work in San Francisco. But the damage was done. He was still apologizing when we put them together on Skype.
MATTHEW (GRANDSON): I felt terrible. I felt like there should have been something that I could have done.
STEVE BAKER (FEDERAL TRADE COMMISSION): This is very, very, very widespread. It's ripping off thousands of people, just ordinary people just like you and me.
DIANE SAWYER : $100 million ripped off last year, Ron. So you want to help your family, what do you do?
RON CLAIBORNE : Well, Diane, the most important thing you can do is have a code word that's known only to family members and your best and closest friends so that if there is a real emergency, they can cite that code word. As you heard, that fake call sounded very much like my real cousin James.
DIANE SAWYER (ABC NEWS)(OC): Amazing.
RON CLAIBORNE : Almost exactly like him. Very convincing.
DIANE SAWYER (ABC NEWS)(OC): Simply amazing, but it's come to this, you have to have a code word for a phone call. Thank you, Ron.