The tragic case of Edna Schmeets is not hard to understand, and is alarmingly common.

The Harvey, North Dakota, woman turned over some $400,000 to telephone con artists who convinced her that the money would allow her to claim a $19 million Jamaican lottery prize. Of course, there was no prize, no lottery and Edna's money went straight to a bunch of crooks. Think you are too smart to get roped into a scam like that? Then the fraudsters already have a leg up on you. In fact, you may have already supplied them the tools they need to begin ripping you off.

The fraudsters who ripped off Edna got her name from a list they had purchased from a Jamaican man, Sanjay Williams, who also had ties to Charlotte, North Carolina. Williams had started out on the front lines of the ubiquitous Jamaican lottery scams, as a telemarketer calling unsuspecting victims. But he found his skills more suited to gathering the victims' names and numbers to begin with.

Not that gathering the information required a whole lot of skill.

According to a 2013 criminal complaint, Williams operated a web site called "gamblersleads.com," selling lists of potential victims — complete with contact information — to telemarketers, raking in hundreds of thousands of dollars. Compiling lead lists for telemarketers is not a crime in itself, of course. But Williams was creating what fraudsters call "sucker lists." And it was as easy as shooting fish in a barrel.

Williams' weapon of choice was direct mail — a common tactic, according to U.S. Postal Inspector Scott Horne.

"The scammers may draft a letter and say if you want to enter into a lottery, then the only thing you need to do is send a payment of $19.99," he tells "American Greed."

Most people consider it junk mail and throw it away. But the ones who comply are perfect candidates for a sucker list. By sending back the post card, the victim has supplied the crooks not only with their identity, but also their contact information and in many cases their bank details. Plus, they have identified themselves as someone who is eager to win the lottery — and believes they really might have a shot.

"It's not a coincidence that it's seniors who are so often targeted," says Steve Weisman, a senior lecturer of law, taxation and financial planning at Bentley University in Boston, and author of the new book "Identity Theft Alert: 10 Rules You Must Follow to Protect Yourself from America's #1 Crime."

"Scam artists are the only criminals we call artists, and they prey on fear and greed," Weisman says.

But even if you are not a senior, or you think you couldn't possibly fall for such a scam, don't let your guard down. That means don't give your phone number to strangers — even if you think it might give you the inside track on a multimillion-dollar lottery prize, which, by the way, it won't.

Of course, there are plenty of other ways for crooked telemarketers to get your phone number, which explains many of the calls that practically everyone gets every day. Answering those calls is, in many cases, not much different from filling out that direct mail lottery card and sending it in. Just by picking up the phone and saying "Hello," you have informed the crook that your phone number is real and someone is home. And you've probably won yourself a spot on one of those sucker lists.

Experts say you should never pick up a call from a number you do not recognize.

"If you get a call and it's from an 876 area code, that's from Jamaica," Weisman cautions. "Unless you've got a relative that's vacationing there, you don't even pick it up."

Jamaica is a hotbed for the lottery scams, to the embarrassment of the Jamaican government, which values the country's ties to the U.S. and would prefer to be welcoming to American tourists. So since 2009, Jamaican police and U.S. authorities have partnered on an anti-lottery task force.

The case of Sanjay Williams — the man who peddled the sucker lists — was a milestone: the first list seller successfully prosecuted in the U.S. He is serving a 20-year sentence for conspiracy, fraud and money laundering.

His 2013 arrest also led authorities to a fraud ring including the people who carried cash to and from Jamaica. Eleven people pleaded guilty.

But authorities say none of that will do any good until people stop taking the bait.

"Have you tried to talk to your elderly loved ones or your parents about their finances? It's not easy," says Jim Stitzel, Jamaican attache with the U.S. Department of Homeland Security, but it is vital. "Have that tough financial conversation because it's better to have it and have a small dust-up now than have it when they've lost their life savings."

Edna Schmeets lost almost everything, until her children intervened.

"What in the hell was I thinking? I wasn't thinking. I can't even believe it. I mean, could you actually be that stupid," she asks.

But in the end, Schmeets helped the authorities bust a multimillion-dollar fraud ring.

Trouble is, there are plenty more where it came from.

"American Greed" Thursdays 10 p.m. ET/PT on CNBC Prime.