Which type of malware is designed to replicate itself and spread to other systems?

A worm is a type of malware that is specifically designed to replicate itself and propagate to other systems without needing to attach itself to a host file. Unlike a virus, which requires a user to execute it in order to spread, a worm can exploit vulnerabilities in network protocols to autonomously move from one computer to another. This autonomous capability allows a worm to spread quickly across networks, making it particularly dangerous in a connected environment.

In contrast, a virus requires interaction with a user or another program to spread, and a Trojan horse disguises itself as legitimate software without self-replication. Ransomware, while also harmful, encrypts files on a victim's system and demands payment, but it does not replicate itself or spread independently. Thus, the defining characteristic of a worm being its self-replicating ability and potential to spread widely provides a clear rationale for why this answer is correct.