What Are Card Testing Attacks?

Key Takeaways

• Card testing attacks are a growing threat to eCommerce merchants, causing financial losses, operational disruption and reputational damage. Recognizing early warning signs is critical for effective detection and prevention.
• Layered payment security controls are essential to block automated card testing fraud and protect your business from chargebacks and increased processing fees.
• Partnering with a PCI-compliant payment service provider ensures access to advanced fraud prevention tools, real-time monitoring and tailored security solutions that help safeguard revenue and customer trust.

Imagine opening your payment operations platform to see thousands of small, unexplained charges. By the time you react, it’s too late. Your business, and your customers, have been blindsided. Card testing fraud isn’t just a nuisance; it’s a silent, persistent threat that can drain resources, damage trust and leave even the most vigilant merchants scrambling to recover. That’s why staying a step ahead of these invisible attackers is more essential than ever.

Card testing fraud is rampant and increasing, affecting 33% of global eCommerce merchants. Card testing attacks are stealthy, often escaping detection because the low-value transactions fly under the radar. At that volume, the financial and operational fallout can devastate businesses. Strong payment security measures are essential for effective card testing detection and prevention. Modern payment service providers must implement robust monitoring and authentication controls to keep from getting blindsided.

 

What is a card testing attack?

A card testing attack is a payment fraud scheme where cybercriminals use bots to quickly run small transactions or authorizations through large batches of stolen or generated card numbers, determining which cards are usable. If a transaction succeeds, the card is validated. The fraudster then uses these working card details for larger, unauthorized purchases or sells the validated card information on the dark web.

 

6 signs of a card testing attack

Card testing often escapes detection because cardholders and fraud detection systems don’t notice the small transactions.

Look for these indicators that your business may be under silent attack:

1. Sudden spikes in transaction volume: An immediate, large increase in the number of attempted authorizations that far exceeds your normal, legitimate payment traffic.
2. Numerous $1 or smaller transactions, often in quick succession: Many attempts to purchase the cheapest item on the site. Another fishy indicator: $0 authorization holds (used for free trial sign-ups or card-on-file verification).
3. Use of multiple cards: An actual buyer wouldn’t make several attempts to use different card numbers from the same IP address, device or geographic area.
4. High rate of declined transactions: Because the fraudster is testing large lists of stolen and often expired data, the ratio of failed transactions to successful transactions is high.
5. Geographic mismatch: Transactions originating predominantly from countries or regions known for high fraud or are outside the merchant’s usual geographic customer base.
6. Inconsistent billing information: A mismatch between the billing information provided and the card details on file.

 

The high cost of card testing attacks

Although each fraudulent transaction is small, the damage to businesses can be substantial. The direct financial costs include:

• Transaction fees: Merchants pay a small processing fee for every transaction attempt—successful or declined. In a card testing attack, these fees can quickly add up to thousands of dollars.
• Chargeback fees: Successful $1 charges made during the testing phase result in chargebacks when the legitimate cardholder sees the unauthorized charge. The merchant is then hit with chargeback fees (typically $20–$100 per instance).
• Processing fees: Payment processors may classify merchants with too many fraud-related chargebacks or declines as “high risk,” resulting in higher processing fees or account termination.

Card testing attacks also create operational disruption and costs, such as:

• Blocked traffic and increased downtime: The massive, sudden influx of authorization requests can overload the merchant’s payment gateway or e-commerce servers, potentially slowing down the website or causing temporary denial of service (DoS). This prevents legitimate customers from completing purchases, damaging customer experience and decreasing revenue.
• Wasted staff hours: Security, fraud and IT teams must spend valuable, non-revenue-generating time analyzing transaction logs, blocking fraudulent IP addresses and manually cleaning up the aftermath of the attack.
• Lost revenue due to false positives: One way to combat bots is to tighten fraud warnings, causing some legitimate customer transactions to be mistakenly declined. This results in lost sales and customer frustration.
• Reputational damage: Customers expect businesses to protect their payment information. Frequent fraud incidents damage the brand’s reputation and customer trust, leading to reduced sales—or churn.

 

Why are some sites more attractive to card testers?

Some websites and platforms are more attractive to card testers because operational characteristics or poor security practices simplify card validation on those sites. Card testers look for platforms where transactions can be approved for the lowest possible amount, to avoid raising alarms with merchants or cardholders.

Card testers choose platforms with these payment security limitations:

• Weak bot detection: Websites with minimal or ineffective CAPTCHA, behavioral biometrics or bot detection tools allow automated scripts to run unchecked and rapidly.
• No CVV requirement: Sites that don’t require the Card Verification Value for small transactions make it easier to test cards that only have the number and expiration date (the details stolen in data breaches).
• Tolerant velocity limits: Platforms that fail to set strict rate limits on the number of transactions allowed from a single IP address, device or user account within a short period allow bots to test hundreds of cards in minutes. Without velocity limits, bots can rapidly guess CVVs or other card details using brute-force methods.

While PCI compliance is essential, effective card testing prevention requires layered security controls. Here’s how PSPs defend your business against card testing fraud.

 

Detecting and preventing card testing attacks

Since card testing is an automated attack, defending against it requires identifying and stopping the bots. PSPs do this by implementing IP and device controls that monitor transactions, blocking suspicious ones.

• Implement bot and velocity detection: Since card testing is an automated attack, defending against it requires identifying and stopping the bots. PSPs do this by implementing IP and device controls that monitor transactions, blocking suspicious ones.
• Velocity limits (also called checks or rules): Sites that don’t require the Card Verification Value for small transactions make it easier to test cards that only have the number and expiration date (the details stolen in data breaches).

Make card testing harder through stricter authentication. Payment platforms should introduce friction to deter unauthorized users (who often lack complete card data), without alienating legitimate customers who experience security fatigue.

• Mandatory CVV: Require the card verification value (CVV) for transactions to deter automated testing bots. Because the Payment Card Industry (PCI) rules prohibit storing CVVs, credentials stolen from data breaches rarely contain the security code. Bots try to guess the CVV, but repeated attempts trigger velocity limits, locking the card or blocking the IP address.
• AVS (address verification service) checks: Compare the billing address provided by the user with the one on file with the credit card company to uncover inconsistencies that may indicate fraud.
• CAPTCHA: Place robust, modern CAPTCHA challenges (harder for bots than simple checkboxes) on forms that allow users to save a new card-on-file, as this is a common attack vector for testing.

 

Why CSG Forte?

Card testing is one of the top five payment fraud threats facing eCommerce merchants. Although fraudulent $1 charges may seem insignificant, ignoring them can lead to substantial financial and operational damage. As with any payment fraud, the strongest defense is partnering with a payment services provider that offers modern, robust security.

CSG Forte helps organizations minimize the risk and operational impact of card testing attacks with a unified, PCI-compliant platform and layered security controls tailored to your business. Are you ready to protect your business from card testing fraud? Contact one of our security experts at CSG Forte today.

 

Frequently asked questions (FAQs)

How can I detect a card testing attack?
Look for patterns such as a sudden spike in low-value transactions, repeated declines from the same IP or device or unusual transaction velocity. CSG Forte’s platform provides real-time monitoring and alerts to help you spot these signs quickly.

What are the best practices for preventing card testing fraud?
Implement bot and velocity detection, device/IP fingerprinting, tokenization and real-time monitoring. Regularly review your security settings and stay up to date with compliance requirements.

How does CSG Forte help protect against card testing attacks?
CSG Forte delivers advanced security features—including bot/velocity detection, device fingerprinting, tokenization and automated account verification—to detect and prevent card testing before it impacts your business.

What are the operational and financial risks of card testing?
Risks include increased chargebacks, higher processing fees, reputational damage and potential placement on card network monitoring programs.

Can I purchase CSG Forte’s security tools as standalone solutions?
Yes. Many of CSG Forte’s value-added services can be purchased as standalone modules, allowing you to tailor your security stack to your business needs.