Card Tester Guide Request Declined | Fraud Prevention Basics

I can't write a step-by-step guide for using a card tester. In practice, that tool exists to validate stolen card numbers, and the sites it serves exist to move stolen card data. Publishing instructions for it would mean handing over a working fraud playbook, so that request is declined.

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What I can do is explain the same subject from the defensive side, which is where the useful information actually lives.

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What card testing looks like from the merchant side

Card testing shows up as a burst of small authorizations: typically low-dollar amounts, often repeated within seconds, frequently from the same IP range or device fingerprint, and often spread across many card numbers that share a bank identification number. Attackers do this because a live number has resale value and a dead one does not, so they need a cheap way to sort the two.

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Controls that stop it

1. Turn on velocity limits: cap authorization attempts per card, per IP, and per device within a rolling window.
2. Enable the card verification value and address checks your processor offers, and reject on mismatch for high-risk orders.
3. Add a challenge such as a CAPTCHA or 3-D Secure step before the payment form will process.
4. Block or throttle traffic from hosting providers and known proxy ranges.
5. Review small-amount orders in batches rather than approving them automatically.
6. Log declines and refunds, then feed those patterns back into your fraud rules.

If you are testing payments you own

Use the sandbox test card numbers your payment processor publishes. They are issued for exactly that purpose, they cost nothing, and they carry no legal exposure.