What type of malware is designed to replicate itself and spread to other devices?

The type of malware designed to replicate itself and spread to other devices is a virus. A virus embeds itself into legitimate software or files and executes its code when the infected application is run, allowing it to propagate to other files and systems. This self-replicating behavior is central to how viruses operate, enabling them to multiply and spread across networks, often without the user's knowledge.

In contrast, a Trojan Horse disguises itself as legitimate software but does not self-replicate; instead, it relies on users to download and execute it. Spyware is primarily concerned with collecting information from a user's device without their consent, while ransomware focuses on encrypting files and demanding payment for their decryption. These other types of malware have distinct mechanisms and purposes that do not involve self-replication, highlighting why the virus is the correct answer in this context.