FRAUD SCENARIO LIBRARY

ACH Fraud

ACH fraud involves unauthorized or fraudulent transfers made through the Automated Clearing House (ACH) network, commonly targeting business or personal bank accounts.

How Does ACH Fraud Work?

Attackers steal bank account and routing numbers through phishing, malware, or using compromised accounts post ATO.

Attackers steal bank account and routing numbers through phishing, malware, or using compromised accounts post ATO.

Attackers steal bank account and routing numbers through phishing, malware, or using compromised accounts post ATO.

They initiate unauthorized ACH debits or impersonate vendors to divert payments.

Often involves account takeover or social engineering tactics to modify payment instructions.

Often involves account takeover or social engineering tactics to modify payment instructions.

ACH Fraud Detection

Spotting Suspicious Withdrawals in Real Time

A small business begins experiencing large unexpected debits from its account. It turns out the vendor details had recently changed - and Unit21’s layered detection caught the manipulation just in time.

1

Fingerprint Flags Reused Login Device

A device associated with past fraud attempts logs into multiple business accounts and initiates ACH transfers. Fingerprint identifies reused IPs and mismatched login geography.

2

Unit21 Risk Rule Triggers for New Payee + Large Transfer

Unit21 detects a first-time ACH transfer to an unverified payee, combined with an unusually high amount and no historical payment context. This triggers a high-risk flag.

3

Behavior and Change Pattern Detected

Unit21 surfaces a behavioral anomaly: the account details were updated just before the transfer, but without re-authentication or confirmation - a classic ATO red flag.

4

Risk Score Spike & Transaction Hold

The affected account is immediately assigned a higher risk score. The transaction is held, and an alert is escalated to fraud analysts before the money leaves the account.

5

AI Agent Builds Regulatory Narrative

Unit21’s AI Agent creates a SAR summary outlining the fraud signals: IP reuse, vendor impersonation, large first-time payment, and lack of verification. A filing is completed in-platform with all linked evidence.

Prevention Tips For ACH Fraud

  • Verify new accounts and changes to payment details.
  • Use risk scoring for ACH transactions and new payees.
  • Monitor for unusual debit patterns or high-risk returns.
  • Enable user alerts for outbound transfers and account updates.
  • Educate users on ACH fraud and dispute options.
FREQUENTLY ASKED QUESTIONS

ACH Fraud

What is ACH fraud and how does it work?
Why is ACH fraud a serious concern for institutions?
What makes ACH fraud hard to catch?
What technical gaps allow ACH fraud to succeed?
What common vendor oversights increase vulnerability?
What types of social engineering are used in ACH fraud?
How can organizations strengthen ACH fraud defenses?

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