What is a common characteristic of a worm in contrast to a virus?

A worm is a type of malware that is distinct from a virus primarily in how it spreads and operates. One of the most notable characteristics of a worm is that it does not infect files directly, which aligns with the chosen answer. Instead of attaching itself to a host file like a virus does, a worm is able to replicate and spread independently across networks.

This allows worms to propagate quickly without the need for human interaction or the existence of a host program, which is where some of the other options diverge from the correct choice. Viruses typically require a user to execute a file for infection to occur, while worms can autonomously spread through vulnerabilities in software or network systems.

Furthermore, while not all worms cause file corruption, and not all of them reside within a host program, their primary function centers around self-replication and network exploitation rather than file infection. Thus, the defining trait of a worm not infecting files directly underscores its difference from viruses and justifies the correctness of the answer.