A _________________ is malicious software that is hidden and packaged inside other software that looks normal and legitimate.

(A) Worm
(B) Virus
(C) Spyware
(D) Trojan

Trojan is the correct answer. A trojan horse is malicious software that is hidden and packaged inside other software that looks normal and legitimate. If a well-meaning user decides to install it, the trojan horse software is silently installed too. Then the malware can run attacks of its own on the local system or against other systems.

Trojan horse malware can spread from one computer to another only through user interaction such as opening email attachments, downloading software from the Internet, and inserting a USB drive into a computer.

Worms are another type of malware that is able to propagate to and infect other systems on its own. They use a computer network to spread, relying on security failures on the target computer to access it, and steal or delete data.

Viruses are malware that can propagate between systems more readily. To spread, virus software must inject itself into another application, then rely on users to transport the infected application software to other victims. Viruses must execute to do their dirty work, so they target any type of file that the system can execute.

Spyware is, as the name implies, software that spies on you. Designed to monitor and capture your Web browsing and other activities, spyware, like adware, will often send your browsing activities to advertisers. Spyware, however, includes capabilities not found in adware. It may, for example, also capture sensitive information like banking accounts, passwords, or credit card information.