What is defined as a self-replicating malicious program that corrupts files?

The correct answer is a worm, which is defined as a self-replicating malicious program that can spread across networks and corrupt files without user intervention. Worms exploit vulnerabilities in software and systems to duplicate themselves, propagating from one computer to another. Unlike other types of malware, worms do not require the host program to be activated by a user; instead, they spread automatically, making them particularly dangerous.

For context, a Trojan horse is designed to appear benign or even useful while actually carrying out harmful deeds once it is executed. Adware is a type of software that automatically displays or downloads advertisements, and while it can be intrusive, it typically does not corrupt files. Spyware is designed to gather information from a user's device without their knowledge, often tracking user behavior or stealing personal information, but it does not have the self-replicating feature of a worm. Therefore, the defining characteristics of a worm align perfectly with the description provided in the question.