Trojan

Taken from Twinkl USA

3. Definition: A Trojan is a seemingly harmless program that appears to perform a useful task (e.g., a game) but, in the background, performs something with negative consequences, such as spying after a user.
   
   The program is either actively installed by a computer's user or administrator, not knowing that the program does a malicious activity, or is installed as a payload of a virus or a worm.
   
   Reason for the name: It is based on the story of the wooden Trojan Horse that was sent by the Greeks into the city of Troy during the Trojan War. The gigantic horse, which was presented to Troy as a gift, was the hiding place of Greek warriors who launched an attack on Troy.
   Propagation: When a user runs the program, it performs the task that the user intends to do in the foreground while also performing a disguised, malicious task in the background, without the user's awareness.
   Examples of well-known Trojans: Flame, Zero Access, Banker, Zeus, and Beast.