The Easiest Fraud Act to Build Is Often the Easiest One for Fraudsters to Bypass

One of the biggest mistakes in fraud prevention is confusing the pattern with the problem. Teams spot an attack, lock onto shared traits - product, vendor, amount - and build a narrow act. Fraudsters then change one detail and slip through. The pattern helps you understand the attack; the real question is the core behaviour that makes it fraudulent, and which signals stay useful after the details change.

The easiest fraud act to build is often the easiest one for fraudsters to bypass.

One of the biggest mistakes in fraud prevention is confusing the pattern with the problem. Fraud teams often solve the pattern. Fraudsters solve the act.

I've seen this repeatedly throughout my career, particularly in e-commerce, where fraud patterns can evolve incredibly quickly.

How over-specific acts fail

A fraud team identifies an attack. They analyse the transactions, find the common characteristics, and build an act to stop it. Maybe every fraudulent transaction involves the same product, maybe they're all coming through one vendor, or maybe the transaction values sit within a particular range.

So you block that product, vendor, or amount. Problem solved - except the fraudster learns too. Once they realise their transactions are being blocked, they don't necessarily abandon the merchant. They change the product, adjust the amount, switch the account, device, or payment method, and find another route through the system - or they move to another merchant that hasn't adapted yet.

This is why one of the biggest mistakes fraud teams can make is building controls that are too closely tied to the exact pattern they're seeing today.

Ask about behaviour, not just fingerprints of the attack

The specific pattern is useful for understanding an attack, but the more important question is: what is the core behaviour that makes this fraudulent?

• Don't just ask how to block transactions buying Product X. Ask why fraudsters are targeting Product X in the first place.
• Don't just block a specific transaction amount. Understand what behaviour separates those fraudulent transactions from legitimate ones.
• Don't keep adding increasingly specific acts every time the attack changes. Look for signals that remain relevant even when fraudsters change the details.

In simple terms, fraud prevention is an evolutionary race. You change one thing, and the fraudsters respond. You learn from their response, and the cycle starts again. The fraud teams that stay ahead are the ones that understand the underlying behaviour well enough that a small change from the fraudster doesn't make their entire defence obsolete.

Related reading: overfitting in fraud prevention, how it works, pricing, and the FAQ.

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Originally shared on LinkedIn.