Fraud Prevention
Promo and bonus abuse: screening numbers at sign-up
A welcome bonus, referral credit or free trial paid per new account is only profitable if each account represents a genuinely new customer. Multi-accounting, one person or bot creating dozens or hundreds of accounts to claim the same bonus repeatedly, depends almost entirely on being able to obtain many phone numbers cheaply and quickly. Screening the number itself at sign-up, before the bonus is granted, is one of the highest-leverage checks a growth or risk team can add.
Why phone number screening works against promo abuse
Most promo abuse operations are constrained by cost and speed, not sophistication. A legitimate customer has one mobile number tied to a real SIM. An abuser running the same sign-up flow at scale needs many numbers, and the cheapest way to get them is a disposable or virtual VoIP number that can be provisioned in seconds. That single property, real mobile SIM versus disposable VoIP line, is exactly what a number type check surfaces before an account is created.
What to check at the point of sign-up
- Number type: mobile numbers tied to a real SIM cost more to obtain in volume than VoIP numbers; flag fixedVoip and nonFixedVoip for extra scrutiny
- Carrier: a cluster of new sign-ups all resolving to the same obscure carrier or virtual network operator is a pattern worth investigating in aggregate, not from a single query
- Active status: a number that is not currently reachable on the network is a weak candidate for a real customer relationship
- Country: a number registered outside the markets a promotion targets is worth an extra check if the offer is geographically restricted
None of these signals proves abuse on its own. A VoIP number is not automatically fraudulent, plenty of real customers use them. The value is in combining the phone signal with existing device, email and payment signals so that only the highest-risk combination triggers a manual review or a delayed bonus payout.
Where to place the check in the flow
Run the lookup as soon as the number is entered, before the account or bonus entitlement is created, so a flagged number never reaches the reward stage.
Mobile numbers proceed through standard onboarding. VoIP and landline numbers route to a stricter path: delayed bonus release, a secondary verification step, or manual review, rather than an automatic rejection that could catch legitimate customers.
The same number, or numbers sharing an unusual pattern, appearing across multiple new accounts within a short window is a stronger signal than number type alone; combine the phone check with your own account-level deduplication logic.
For the sign-up-specific implementation pattern, including a working code example, see blocking disposable numbers at sign-up.