The US's largest bank has contacted these customers by post, informing them that their cards are no longer valid, and warning them to check their bank statements for unauthorised transactions.
Details regarding this move are currently hazy, as the bank has refused to confirm which firm was involved in the breach or even what type of establishment it is, nor has it confirmed the number of customers involved.
A bank spokesman said: "These are intricate matters... and may involve information that is not exactly clear and concise. It would be premature to discuss any third parties until an investigation is conducted."
However, he did claim that the cancellation of the cards was merely precautionary and that there was no efforts to suggest that the accounts of any of their customers had been compromised.
This episode is something of an oddity, as most cases of fraud involve credit cards, which are far more commonly used for retail purchases, rather than debit cards.