From the moment the miles-and-points game was invented, mileage junkies have been on the lookout for ways to beat the system. Recently, they seem to have stumbled upon a doozy.

For months now, banks across the country have been issuing Visa and MasterCard “gift cards” — pre-paid cards that are accepted by merchants as credit cards.

One bank in particular — Cleveland’s Charter One Financial — has sold more than 600,000 of the cards in November and December, according to The Wall Street Journal.

The racket is simple: A consumer purchases, say, a $500 card with his or her regular mileage-earning credit card, and, because the transaction is treated as a purchase by most credit card companies (American Express notably excluded) the consumer pockets the miles. He then uses the gift card to buy a money order, which is in turn deposited in the bank and used to pay the credit card bill. The consumer is only out the one- or two-dollar fee for the money order, and is 500 miles richer.

Charter One is apparently unfazed by this increasingly popular mileage-earning scheme, which only makes sense, since it is the consumer’s “real” credit card company that’s paying for the mileage. Nevertheless, Charter One has placed a $5,000-per-month cap on purchases, even if, according to The Journal, that restriction is loosely enforced.

Consumers should be aware that, though the practice is perfectly legal, there are some potential dangers involved.

According to The Journal, repeated expenditures for gift cards could set off a “fraud alert,” which could result in the card being temporarily disabled. You’ll need to call the credit card company personally to explain the situation.

Secondly, it is conceivable that your credit card company could suddenly begin treating the purchases as cash advances. A potential defense could be to call your card company and ask them to disable any cash-advance ability your card might have.