Gift cards are one of the easiest – and most popular – presents this holiday season.

But, before you pick up that stack of cards at your local retailer, law enforcement and other officials are warning of a new scam that could make presents worthless.

The scam works like this:

Criminals record the card and PINS from unpurchased gift cards, and then place them back in the packaging. They then wait until the card is purchased and activated – information they can find online – and use the card until it’s “drained.”

Avoid buying gift cards from online auction sites because they may be fake or stolen.

Keep your store receipt in case the gift card you’ve purchased is later compromised. You can also take a picture of the gift card and store receipt. The number on the gift card and store receipt will help you file a report with the gift card company if you lose the gift card or if you need to report fraud.

If you purchased a gift card that is used by a scammer, report it to the gift card company directly, request a freeze on the card and a refund. You can find contact information for some of the more popular gift card companies here.