This rule identifies credential testing attacks where fraudsters attempt to validate stolen card numbers through rapid authorization attempts.

Triggers when:
1. More than 10 declined transactions occur at the same merchant
2. All declines occur within a 20-minute window
3. Pattern indicates systematic validation testing

This attack pattern indicates:
- Fraudster has batch of stolen card numbers
- Testing which cards are still active/valid
- Attempting different amounts to find authorization threshold
- Using compromised terminal or merchant account for testing
- Classic carding operation behavior

System generates an ALERT to enable:
- Merchant account verification
- Terminal security check
- Pattern analysis for fraud ring identification
- Potential law enforcement notification for organized fraud activity