Which approach should an ethical hacker avoid to maintain passive reconnaissance?

CEH v13 defines passive reconnaissance as information gathering without interacting directly with the target or alerting them. The goal is to remain undetected while collecting intelligence from publicly available sources.

Directly interacting with a threat actor on forums—even under a pseudonym—constitutes active engagement. CEH v13 warns that such interaction risks exposure, attribution, and legal complications. It can alert the adversary, cause them to alter behavior, or even retaliate.

WHOIS lookups, DNS queries, archived web content, and anonymous browsing are all passive techniques endorsed in CEH v13. These methods do not notify the target and leave minimal trace.

Thus, Option A should be avoided to maintain a low profile.