The mystery of a tiny charge on credit and debit cards is heightening to one of anticipation - of when the other shoe is going to drop.

Fraud experts are concerned about these charges - from 21 cents to 48 cents - that have appeared on cardholders' accounts in at least 46 states. The fear is someone is trying to find usable card numbers so that they can use the cards to make bigger charges at some future date.

The small charge, showing up as being from either Adele Services or GFDL, is designed to try to fly under the radar of credit card companies' fraud detection programs. Those companies appear to be fictitious.

"More than likely, the perpetrators are attempting to test the waters," said Jeremy Cannon of the National White Collar Crime Center. "They are relying on their assumption that the victim will not be vigilant in monitoring their banking and credit statements."

The scope of this scam has caught the attention of the companies and the national Internet Crime Complaint Center (www.ic3.gov), run by the National White Collar Crime Center and the FBI. The site registered 800 formal complaints about the scam as of last week and officials issued a warning to consumers.

Separately, the consumer finance site Mint.com notified 800 of its customers that a scan of their databases detected those charges on their credit or debit statements. Consumer complaint experts say those who complain tend to represent a tiny portion of those affected, particularly in cases such as this where many would not even know they had been affected.

Ben Woolsey of CreditCards.com warns: "Consumers who have seen these micro charges should be doubly vigilant in monitoring their statements.

It might also be prudent for consumers who experience these charges to report their card as lost and request that a new card with a new account number be issued by their bank" rather than just requesting that the 25 cents be reversed.

Banks are reluctant to discuss such problems for fear of losing customers and increasing costs, he said. Bank of America, for example, said it is against policy to discuss any specific charge.

Chase Card Services vice president Gail Hurdis said she is aware of the charges and said the company has "sophisticated systems to monitor and detect fraudulent activity" and encouraged consumers to promptly call their card's toll-free number if they suspect fraud.

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