Enrage Tech Company hired Enrique, a security analyst, for performing threat intelligence analysis.

Passive DNS monitoring involves collecting data about DNS queries and responses without actively querying DNS servers, thereby not altering or interfering with DNS traffic. This technique allows analysts to track changes in DNS records and observe patterns that may indicate malicious activity. In the scenario described, Enrique is employing passive DNS monitoring by using a recursive DNS server to log the responses received from name servers, storing these logs in a central database for analysis. This approach is effective for identifying malicious domains, mapping malware campaigns, and understanding threat actors' infrastructure without alerting them to the fact that they are being monitored. This method is distinct from active techniques such as DNS interrogation or zone transfers, which involve sending queries to DNS servers, and dynamic DNS, which refers to the automatic updating of DNS records.References:

SANS Institute InfoSec Reading Room, "Using Passive DNS to Enhance Cyber Threat Intelligence"

"Passive DNS Replication," by Florian Weimer, FIRST Conference Presentation