Which of the following is a process of searching unauthorized modems?

Espionage refers to the covert gathering of secret or confidential information, typically for intelligence or competitive purposes, and is not a specific technical scanning technique.

Wardialing uses software to automatically dial large blocks of phone numbers and records which numbers respond with modem carrier tones, allowing an attacker or auditor to discover unauthorized or rogue modems connected to an organization's internal network. It was classically used to find entry points that bypass perimeter firewalls by exploiting forgotten dial-up connections.

System auditing is a formal, structured review of IT systems to assess security controls and policy compliance, not a method for discovering unauthorized modems.

Scavenging involves searching through discarded or leftover data and physical materials (similar to dumpster diving) to recover sensitive information, not locating modems.