Which of the following represents a common feature of a worm?

The reason "it can spread across a network independently" is the correct choice relates to the fundamental characteristics of a worm in the context of computer security. Worms are a type of malware designed to replicate themselves and spread to other computers without needing to attach themselves to existing programs or require a host. This autonomy allows worms to propagate across networks, effectively exploiting vulnerabilities in networked systems.

Their ability to move independently is what differentiates worms from other types of malware, such as viruses, which do need a host file to replicate and spread. The distinctive behavior of worms makes them particularly dangerous, as they can quickly multiply and infect many systems in a short period without human interaction or additional files.

In contrast, the other options reflect behaviors or characteristics typical of different forms of malware. For instance, requiring a host or user action indicates features of viruses or trojans rather than worms. Thus, the unique self-replicating nature of worms is accurately captured by the idea that they can spread independently across networks.