The correct option is D. Trojan horses. Explanation of the Correct Answer What are Trojan Horses? A Trojan horse is a type of malicious software (malware) that disguises itself as a legitimate program or file to trick users into installing it. Once installed, it can perform various harmful actions without the user's knowledge. The term "Trojan horse" comes from the ancient Greek story where the Greeks used a deceptive wooden horse to infiltrate the city of Troy. Trap Doors and Bombs: - Trap Doors: Also known as backdoors, these are hidden methods of bypassing normal authentication or encryption in a computer system. They allow unauthorized access to the system, often installed by malware like Trojan horses. - Bombs: In the context of computer security, "bombs" can refer to logic bombs, which are pieces of code that execute under certain conditions, often causing harm to the system or data. These can also be part of a Trojan horse's functionality. Why Trojan Horses Fit: - Both trap doors and bombs can be components of a Trojan horse. A Trojan may install a trap door to allow the attacker to access the system later, and it may also include a logic bomb that triggers harmful actions based on specific conditions (like a certain date or the presence of a specific file). Explanation of Why Other Options Are Incorrect A. Adware: - Adware is software that automatically displays or downloads advertisements when a user is online. While it can be annoying and intrusive, it is not inherently malicious like a Trojan horse. Adware typically does not include trap doors or bombs; its primary function is to generate revenue through advertising. B. Computer Worms: - Computer worms are standalone malware that replicate themselves to spread to other computers. Unlike Trojan horses, worms do not need to attach themselves to a legitimate program. While worms can cause damage and may have malicious payloads, they do not typically involve the deceptive tactics of disguising themselves as legitimate software, nor do they usually include trap doors or bombs as part of their primary function. C. Firewall: - A firewall is a security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Firewalls are protective measures, not malicious software. They do not involve trap doors or bombs; instead, they are designed to prevent unauthorized access to or from a private network. Summary of Key Points

• Trojan horses are deceptive malware that can install trap doors and logic bombs.
• Trap doors allow unauthorized access, while bombs execute harmful actions under specific conditions.
• Adware is primarily for advertising, worms replicate without needing a host, and firewalls are protective measures, not malware.
• Understanding the characteristics of different types of malware is crucial for identifying and mitigating security threats.

Revision Summary

• Trojan horses disguise themselves as legitimate software and can contain trap doors and bombs.
• Trap doors allow unauthorized access, while bombs execute harmful actions based on conditions.
• Adware, worms, and firewalls serve different purposes and do not fit the definition of trap doors and bombs.
• Recognizing the differences between types of malware is essential for effective cybersecurity.