O.K., America -- raise your hands if you've ever opened up your credit card bill and saw a charge you didn't expect.

It could be a so-called "free trial" charge, where a company (think credit repair firm or a magazine or website subscription) starts charging your for a service you'd forgotten about and don't want. Or, more suspiciously, it might be a tip on an expensive dinner in town that's much higher than you recalled.

If so, you're not alone. According to the new Capital One Second Look survey, 53% of U.S. adults have experienced "surprise" by a mystery charge on their credit card.

"A free trial that may turn into reoccurring charge was the most likely unwanted charge to surprise Americans (36%) and a tip that was larger than a customer remembered giving was the least (18%)," Capital One notes in an email to TheStreet.

Unwanted credit card charges can be a big problem for financial consumers, especially women. "About half (52%) of credit card users, especially women, are more concerned about mistaken or unwanted charges compared to a year ago," notes Nicole Lapin, a personal finance expert who works with Capital One. "That's rightfully so -- unwanted charges often go unnoticed, which can throw people off their budget or monthly spending plan."

Lapin says it's no surprise that, according to the survey, a free trial that turned into a recurring charge was the most likely unwanted charge to surprise Americans (36%). But additional charges are mounting up, too. "Other types of unwanted charges include significant increases in monthly bills or charges that renew automatically -- think your cable bill going way up," she adds. "Then, there's a 'larger than you remember' tip, or duplicate charges -- multiple charges for the same amount at the same merchant, on the same day."

Some companies that charge credit card users are getting particularly creative, and secretive, too. "Airport hotspots are notorious for charging a $10 fee and then, in the fine print, also charging you between $4 and $5 per month for future Wi-Fi use," says Mike Catania, chief technology officer at PromotionCode.org. "There's not a separate box to indicate any fee structure, so click on the terms of service and do a quick search for the 'month' or 'recur' in addition to checking your statement."

As a larger rule, there is a big first step to take when you discover an unwanted credit card charge and don't want to pay it. "Credit card holders have zero liability for unauthorized charges from the four large card networks - American Express, MasterCard, Visa and Discover," says Louis DeNicola, head of content for Saveful.com. "If there's an extra charge on someone's card, they should report it to the card issuer -- sometimes cardholders can do this from the company's online portal -- and they should get their money back."


There are some structural changes you can make to thwart repeated attempts to raid your credit card account, as well.

"The best way to avoid unwanted credit card charges, especially online, is to create a one-use credit card number that is used only for that transaction," explains Steven J. Hausman, Ph.D., and president of Hausman Technology Presentations in Gaithersburg, Md.

Bank of America, for example, has a service called ShopSafe, which is available for online banking customers that creates a card number for a specific dollar amount you specify and for a specific expiration date, Hausman notes. "Any attempt to use the card more than once will be rejected by the bank, and your original credit card number will never be revealed."

"It's also possible to use this card for recurring payments with a dollar cap," he adds. "If a website asks for a credit card number before letting you make a 'free' purchase. you can also create one for a dollar limit of $0.01 - it's not free, but it's certainly a card that would limit your liability."

Other card providers are pitching in to help consumers thwart unwanted charges, too. Eligible Capital One cardholders are automatically enrolled to receive Second Look notifications which alert them of any unusual, duplicate charges, and any increases in recurring monthly charges, like your cable bill. "While its always important to keep track of your credit card charges, sometimes you need a second set of eyes," says Lapin. "Gone unchecked these unusual transactions could end up costing customers hundreds of dollars."

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