What is the difference between a virus and a worm?

The correct choice highlights an important characteristic of viruses: they require user action to spread. This means that a virus typically needs some form of human intervention, such as opening an infected file or running a malicious program, to initiate its spread to other systems. The user’s action triggers the virus, allowing it to execute its code and propagate. This reliance on user behavior distinguishes viruses from worms.

Worms, on the other hand, are designed to propagate independently without user assistance, often exploiting vulnerabilities in network protocols or software to spread across systems automatically. Unlike viruses, worms can replicate themselves and distribute throughout networks, making them a different breed of malware.

The remaining options point out misconceptions or incorrect definitions related to malware. Worms are indeed capable of self-replication, and they don’t typically hide within programs but rather operate across systems autonomously. Also, a virus is not classified as a type of hardware error, as it refers specifically to malicious software that infects files and programs. Thus, understanding that a virus's dependency on user action is what sets it apart is crucial in distinguishing these two types of malware.