Comprehensive and Detailed Explanation From Exact Extract:

A Trojan horse (or simply “Trojan”) is a type of malware that pretends to be legitimate or useful software to trick users into installing or running it. Once executed, it can create backdoors, download additional malicious components, or allow unauthorized access to the system, while often hiding its true purpose.

Why B is correct: A Trojan disguises itself as something benign or helpful (such as a free utility, game, or update) in order to deceive the user and gain access. This matches the definition given in standard cybersecurity sections of IT management materials.

Why the others are incorrect:

A. Keylogger – Specializes in capturing keystrokes to steal information like passwords; it may be delivered by a Trojan, but the defining behavior is keystroke logging, not masquerading as legitimate software.

C. Spyware – Secretly monitors user activity and sends data to an attacker; it focuses on surveillance, not necessarily on pretending to be legitimate software as its core characteristic.

D. Rootkit – Designed to hide the presence of malware or attackers by modifying system processes and tools; its main role is stealth and persistence, not initial disguise as legitimate software.