Multi-accounting detection: find duplicate accounts by device

Updated

Multi-accounting is one person creating several accounts to claim a free offer again, get around a usage limit or a ban, or game a referral or voting system. Detect it at sign-up by checking the device, the normalised email and the network together: one free offer per device and per email, a cap per network, and a human check for new or suspicious devices.

Why one person opens many accounts

  • Repeat free trials, sign-up credits and first-order coupons.
  • Usage limits on free plans or anonymous tools.
  • Coming back after a ban or a chargeback.
  • Referral rewards, votes, reviews or giveaway entries.

Email checks catch less than you think

Gmail ignores dots and everything after a plus sign, so [email protected] reaches the same inbox as [email protected]. Many providers support plus-addressing, and disposable inbox services hand out new addresses in seconds. Normalise emails before comparing them and block disposable domains, but do not rely on email alone.

Detect duplicate accounts by device

A server-verified device ID stays the same when someone clears cookies, opens a private window or uses a new email. Allow each free offer once per device, and link browsers on the same computer through a cross-browser machine signal. In apps, platform identifiers and attestation (Play Integrity, App Attest, DeviceCheck) do the same job and also confirm the app is genuine.

Use the network carefully

Counting sign-ups per IP address catches account farms but also hits families, offices and universities. Cap claims per network over a long window, treat mobile carrier IPv4 addresses (shared by many customers) separately, and give datacenter and VPN addresses a stricter path such as a mandatory human check.

Multi-accounting detection with FingerPrint Checker

FingerPrint Checker combines these checks in one decision at sign-up or when a free offer is claimed: one claim per device and per normalised email, disposable domain blocking, a per-network cap, hourly IP, subnet and ASN limits, and a human check by Turnstile or proof-of-work. It answers allow, deny or a human check, and every account starts with 2,000 free checks.

Frequently asked questions

How can I tell if two accounts belong to the same person?

Compare the devices they signed up and logged in from. The same device ID, or two browsers on the same machine, is strong evidence; a shared IP address alone is not.

Will blocking duplicate accounts hurt real users?

Not if weak evidence leads to a human check instead of a deny, and hard denies are kept for a device or email that has already claimed the offer.

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Every new account gets 2,000 free checks. No card required to start.

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