Which of the following best defines a computer virus?

The definition of a computer virus that is most accurate describes it as a program that reproduces by modifying other programs. Computer viruses are malicious software designed to attach themselves to legitimate programs or files. Once embedded, they replicate their code and often spread to other systems, leading to a range of issues from data corruption to unauthorized access to a user's system.

This characteristic of modifying other programs is essential to understanding how viruses operate. They don't just exist as standalone entities; instead, they rely on host programs to execute their code, thus spreading and infecting more files or systems. This reproductive ability is a key defining feature of a virus compared to other forms of malware.

In contrast, the other options presented do not accurately represent a computer virus. Describing a virus as a harmless program overlooks the fact that viruses harm systems and data. Similarly, a program meant to manage network traffic is a function of network management software, not a virus. Lastly, a type of data backup process suggests a method of data preservation, which is the opposite of what a virus does, as it typically damages or deletes data rather than preserving it.