Which statement best defines a Trojan?

• A. A type of malware that is delivered by email and self-replicates.
• B. Also referred to as Trojan horse. A type of malicious software that when installed, allows a user to perform a normal function while the Trojan performs malicious functions to the computer system without the user's knowledge.
• C. A software utility that encrypts data on disk.
• D. A network protocol used for remote management.

Answer: (B)

A Trojan is malware that hides its malicious activity inside what appears to be legitimate software. The crucial idea is that the user can use the program normally, while secretly the Trojan performs harmful actions in the background, often giving an attacker control or access to the system. It doesn’t usually spread by itself or replicate like a virus or worm; it requires the user to install it, typically through social engineering or by bundling with trusted software.

This matches the described statement: when installed, the Trojan lets the user perform a normal function while the Trojan conducts malicious tasks without the user’s knowledge. Other descriptions describe self-replication (virus/worm), ransomware that encrypts data, or a network protocol, which are not characteristic of a Trojan.