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By Herb Weisbaum

Phone fraud is a highly lucrative crime. Americans lose a staggering amount of money this way, but with millions of victims, it’s hard to tally the losses. A new report provides some estimated numbers.

The online survey, conducted by The Harris Poll for Truecaller, found that 17.6 million Americans lost an estimated $8.6 billion to phone fraud in the last 12 months. The average loss was $489.

“We think the actual dollar number lost may be even higher due to factors like unreported fraud and unchecked phone bills,” said Alan Mamedi, CEO of Truecaller, in a statement. Truecaller, based in Stockholm, Sweden, makes a free app that allows smartphone users to identify incoming calls and block spam.

When those who gave money to a phone scammer were asked how the fraudster contacted them, nearly half (49 percent) said on their cellphone, 36 percent said at home or landline phone and the rest couldn’t remember.

Related: The 5 most common phone scams and how to avoid them

For some reason, men were far more likely to lose money this way, with victims being 71 percent male and 29 percent female.

A separate online survey found that 20 percent of people with smartphones — a prime target for phone fraud — did not do anything to protect themselves. The majority (63 percent) said they simply ignored calls from unknown numbers. Another 31 percent said they search online for suspicious numbers before returning a call.

One of the most alarming findings is how rarely people check their phone bills to spot potential fraud — even those who said they received a call from a scammer or suspicious/unknown number. Keep in mind that some phone scams involve placing unauthorized charges on the victim’s phone bill.

More than half said they never (33 percent) or rarely (21 percent) check their phone bill. Of those who did check, 37 percent found fraudulent charges.

“We’re seeing that a lot of smartphone owners are not taking some very essential steps to avoid becoming mobile scam victims,” Mamedi said. “Scam artists are only going to get smarter about how to conceal their identity, and consumers will need better and easier ways to prevent scams.”

How to spot and avoid phone fraud

Con artists are good at selling their lies — they do this for a living. So you always need to be on guard.

“Be skeptical and suspicious of all calls,” said Jean Mathisen, director of AARP’s Fraud Fighter Call Center. “When you pick up the phone, you cannot assume the person is who they say they are.”

If it sounds like something that might be important, such as your bank or credit card company calling, hang up and call them back at the number you know is reliable, such as the one on your credit card or bank statement, not number the caller gives you.

“Don’t give any personal information over the phone to anyone, unless you’re absolutely sure you know they are who they say they are,” warned John Breyault, director of the National Consumers League’s website.

Beware of spoofing

Caller ID can be a helpful way to screen calls, but you can’t trust it.

“It’s very easy for scam artists to make your caller ID display any number they want. It’s called spoofing,” Breyault explained. “They can make it look like they’re calling from anywhere in the U.S. when they are actually overseas.”

They can also spoof the name and phone number of a bank or government agency, even the local police department, to make the call appear legit.

If the call sounds suspicious or you just aren’t interested in what the person is pitching, get off the phone.

“No matter how confident you are that you won’t share any personal information, the longer you stay on the phone, the more likely you are to say more than you intended,” Mathisen cautioned. “You don’t have to be rude, just say ‘no thanks’ and hang up.”

The Federal Trade Commission has tips on how to spot and avoid phone fraud on its website.

Herb Weisbaum is The ConsumerMan. Follow him on Facebook and Twitter or visit The ConsumerMan website.