What is the Visa VAMP enumeration threshold?

Under Visa's Acquirer Monitoring Program, a merchant is identified for enumeration when 20% or more of its authorization attempts are flagged as card testing, with at least 300,000 enumerated attempts in a month.

What enumeration means

Enumeration is a form of card testing where fraudsters try many card numbers, often generated in sequence, to find valid ones. Visa flags attempts it identifies as enumeration and counts them per merchant.

How the threshold works

Both conditions must be met in the same month: a high share of flagged attempts and a large absolute number. The high volume floor means the threshold targets merchants under a real attack.

Consequences

An identified merchant and its acquirer face program fees and must take remediation steps. Acquirers watch these signals closely across their portfolio.

How merchants avoid it

• Velocity limits on cards, devices and IPs.
• Bot detection on the payment page.
• 3-D Secure for suspicious attempts.
• Monitoring of authorization and decline rates in near real time.
• Reacting fast when an attack starts.

Separate from fraud and dispute ratios

VAMP also measures fraud and disputes together. Enumeration is tracked as its own signal.

What it means for payment operators

For you, monitoring declines and attempt patterns per merchant is the early warning. Supervision dashboards and velocity rules you can tighten at once help keep your merchants well below the threshold.