This rule detects high-volume coordinated card fraud attacks using large batches of cards from the same issuing institution.

Triggers when:
1. 20 or more unique card numbers used at single merchant
2. All cards have identical BIN (first 6 digits)
3. Concentrated within 30-minute time window

This elevated threshold indicates major fraud activity:
- Large-scale data breach monetization
- Professional fraud ring operation with significant card inventory
- Compromised POS system being used for rapid bulk processing
- Money laundering operation using multiple accounts
- Merchant collusion with organized crime

Volume of 20+ cards suggests:
- Immediate law enforcement notification warranted
- Critical issuing bank alert needed
- Merchant account suspension consideration
- Pattern likely indicates ongoing criminal enterprise

System generates high-priority ALERT requiring immediate fraud team intervention and potential emergency merchant/terminal lockdown.