As many as 40,000 Target gift cards could be faulty, spelling trouble for the US retailer as it struggles to recover from a data breach.

Some of the gift cards sold during the holiday season will not activate properly, although the number of cards affected is thought to be less than 1% of the total cards sold during the period.

Target spokeswoman Molly Snyder confirmed the problem, saying: "We are aware that some Target gift cards were not fully activated and apologise for the inconvenience."

Target would not confirm how many cards were faulty, but asked affected customers to visit an in-store customer service centre or call the phone number on the reverse of the card.

This latest glitch comes on the tail of a massive data breach that saw the credit card details of 40m customers compromised, leading some banks and credit unions to immediately cancel and replace their cards.

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