Richard Drew, AP
In this May 9, 2012 file photo, a Visa credit card is tendered at opening of the Superdry store in New York's Times Square. Americans boosted their borrowing in August by the largest amount in three months with strong gains in the category that covers auto and student loans and in credit card debt.

"Zombie subscriptions," a hidden credit card charge method, could be haunting your bill, according to an NBC News article.

This is one of six “gray charges,” which are costs merchants add that the consumer is unaware of and generally would cancel them if they knew.

These charges are usually $12 to $18, but added up to an annual cost of about $358.

"I am surprised by the amount of legitimate companies — well-known companies — that have repeatedly confused and deceived customers into paying," said Yaron Samid, CEO of BillGuard, to NBC News.

Unwanted and misunderstood subscriptions

This accounted for almost half of the gray charges. For example, 3 million people still paid AOL for dial-up Internet Access service last summer because of automated-monthly billing. BillGuard didn't know how many costumers used dial-up, but once customers found out about the charges, usually they turned off AOL.

Zombie subscriptions

After a service is canceled, it "comes back to life" when the consumer doesn't want it. What also comes back to life? The charges.

Unwanted auto-renewals

Consumers forget to cancel a product before an annual renewal and after the charge is placed on their card, it is too late to cancel.

Free-to-paid services

A service may start out free, but sometimes a free trial automatically becomes a paid service without a consumer realizing it.

Cost creep

Monthly purchases have a gradual increase each month. One month it's one more dollar, the next another, and so on.

Negative option marketing

This includes various methods for merchants to enroll consumers in agreements. For example, receiving a second unwanted service that is packaged in with a legitimate purchase.

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