What defines a computer worm?

A computer worm is specifically defined as a type of malicious software that has the capability to replicate itself in order to spread to other computers. Unlike viruses, which attach themselves to legitimate programs or files and require user action to propagate, worms can move through networks and autonomously exploit security vulnerabilities to create copies of themselves across multiple systems. This self-replicating behavior is what distinguishes worms from other types of malware, as they can proliferate without any direct action from a user.

The other options do not accurately characterize what a worm is. For instance, a program that appears useful but contains hidden damage-causing code describes a trojan horse, while suspicious software is too vague to define any specific kind of malware. Additionally, software that solely displays advertisements relates to adware, which is also distinct from the self-replicating mechanism seen in worms. Understanding this definition helps in identifying and mitigating the risks associated with worms in cybersecurity.