Concept:Trap doors and logic bombs are malicious code hidden inside software, which are classic types of trojan horses.Explanation:A trojan horse is a harmful program that disguises itself as a legitimate file or application.A trap door is a hidden weakness or backdoor in a program that lets an attacker bypass normal authentication and gain secret access.A logic bomb is a piece of code that stays inactive until a specific condition or event triggers it to cause damage.Both of these are common techniques used within trojan horse programs to harm a computer system.They are not adware, computer worms, or firewall components.Answer:D. trojan horses