For decades, a request for a wire transfer through Western Union or MoneyGram has been the calling card of scammers. But with many would-be victims having finally wised up to that red flag, fraudsters are increasingly asking to be paid in another way: through Green Dot’s MoneyPak cards.

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Available at more than 50,000 retail locations, MoneyPak cards cost about $5. Consumers pay cash to put dollar value on the cards, which can then be used for such things as topping off a PayPal account, paying certain utility bills and funding about 120 brands of reloadable prepaid debit cards — which includes the new AARP Foundation PrePaid MasterCard from Green Dot. Prepaid cards function like traditional checking account debit cards, without the checks.

A MoneyPak comes with a scratch-off 14-digit serial number. To transfer funds to a prepaid debit card, holders call or visit the MoneyPak or Green Dot websites and reveal the number.

And that’s where scammers step in. “Fraudsters will call or email you, saying that you won a lottery or can buy discount merchandise at their phony websites — but you need to pay fees to get your prize or purchase that merchandise via MoneyPak — and only MoneyPak,” says Green Dot spokesman Brian Ruby. “They then ask for the 14-digit code.”

Reveal that — in spite of a warning on MoneyPak cards not to do it — and the crooks can then transfer your MoneyPak funds to their own prepaid debit cards, typically opened under stolen identities, to make their own purchases or ATM withdrawals.

As Scam Alert previously reported, scams using MoneyPak initially appeared in 2009 as a way to get unsuspecting victims to pay “finder’s fees” to secure nonexistent government grants. The timing was not coincidental: At the time, the Federal Trade Commission was cracking down on wire-transfer scams.

MoneyGram, the second largest wire-transfer company, faced accusations from the commission that it had knowingly allowed fraudulent telemarketers to use its system to bilk consumers out of tens of millions of dollars. MoneyGram reached an $18 million settlement with the FTC in that case.

Next: You need to treat your MoneyPak like cash. »