Which of the following is true about viruses?

Viruses are unique pathogens that require a host cell to replicate and produce new virus particles. They do not possess the cellular machinery necessary for reproduction on their own. Instead, once a virus infects a living cell, it hijacks the host's cellular processes to replicate its genetic material and produce viral proteins. This reliance on host cells is a defining characteristic of viruses, distinguishing them from other types of pathogens, such as bacteria or fungi, which can replicate independently.

The other statements in the question do not accurately describe viruses. For instance, viruses are not solely composed of DNA; they can also have RNA as their genetic material. Additionally, they cannot reproduce outside of a host cell because they lack the necessary cellular structures and functions. Furthermore, viruses are classified as non-living entities because they do not exhibit characteristics of life when not within a host, such as cellular metabolism and independent reproduction.