A network traffic analyzer (also known as a packet sniffer) is the best tool to identify credentials being transmitted in plaintext, such as those used in Telnet sessions. Since Telnet transmits data without encryption, a network traffic analyzer can capture the traffic between the client and the network switches, revealing sensitive information, including login credentials, in clear text. This tool helps identify insecure protocols and enables remediation by switching to encrypted alternatives like SSH. CASP+ highlights the importance of using secure protocols and tools like traffic analyzers to identify vulnerabilities in network communications. References: CASP+ CAS-004 Exam Objectives: Domain 2.0 - Enterprise Security Operations (Network Traffic Analysis and Insecure Protocols) CompTIA CASP+ Study Guide: Monitoring Network Traffic for Plaintext Credentials