Fraud Prevention

Loan stacking and application fraud signals

Loan stacking is when a borrower applies to several lenders in a short window, before any single lender's records or a shared bureau can reflect the new debt from the others. Fraud rings run the same pattern at scale using disposable phone numbers and synthetic details to pass each lender's onboarding checks independently. A carrier and number type lookup at the application step flags the number-level tells before the application ever reaches underwriting.

Why the phone number is a useful signal here

Loan stacking and application fraud rings need a working phone number at each application to receive a one-time passcode or a callback verification. Disposable and low-cost non-fixed VoIP numbers are cheap to provision in bulk, which makes them the default choice for an operation running dozens of applications in parallel. A legitimate applicant, by contrast, is overwhelmingly likely to be applying from a standard mobile line they have held for some time.

What to check at the application step

• Number type: non-fixed VoIP, toll-free and voicemail-only lines are disproportionately represented in application fraud and are cheap to acquire in volume. See number type detection for fraud for how each type maps to risk.
• Active status: a number that does not resolve as reachable on the network at the moment of application is a strong signal that it exists only to receive a single verification code.
• Carrier and country consistency: a mismatch between the number's country and the applicant's stated address or the lender's operating market is worth a manual look, particularly alongside other risk signals.

The account takeover variant

A related pattern targets existing customers rather than new applicants: an attacker takes over an active account, often via a SIM swap, then applies to increase a credit line or draw down an existing facility before the account holder notices their phone has lost signal. This is the scenario covered on SIM swap signals for FCA affordability and lending checks, which goes into the regulatory framing for UK lenders in more detail.

Where this sits in the application flow

The most useful point to run a phone lookup is immediately on submission, before the application is scored or routed to manual underwriting review. At $0.03 per query, checking every application is cheap relative to the cost of a single successful stacking attempt, and the result can feed directly into an existing risk score alongside device, bureau and behavioural signals rather than replacing them.