CEH v13 explains that a keylogger is a type of spyware designed to capture user input covertly, often storing or transmitting captured data—such as passwords, emails, chat messages, and financial information—to an attacker. Keyloggers can be implemented as software, firmware, or hardware, and they operate silently in the background without affecting system performance, making them ideal for credential theft. CEH categorizes keyloggers under spying and monitoring malware frequently used in the System Hacking phase to escalate privileges or move laterally once credentials are harvested. Unlike rootkits, which hide processes, or ransomware, which encrypts files, a keylogger’s main purpose is passive surveillance. CEH emphasizes how attackers deploy keyloggers post-compromise or use phishing/social engineering to trick victims into installing them. Their covert nature and ability to bypass traditional AV solutions by masquerading as legitimate processes make identifying them crucial during forensics and incident response activities.