What characteristic defines a computer virus?

The defining characteristic of a computer virus is its ability to reproduce itself within a system. This self-replicating nature allows a virus to spread to other files, programs, or systems once it successfully infiltrates a host. A virus typically attaches itself to legitimate software or files, enabling it to execute its payload and create copies of itself, which can then spread further.

While a virus does indeed infect files and can do so without user consent, the critical aspect that distinguishes it from other types of malware or malicious software is its capability to reproduce and propagate within a system autonomously. This self-replication is what defines it as a "virus," resembling a biological virus that spreads by replicating within living cells.

Although viruses can affect operating systems, they are not limited to them; they can infect a variety of file types, including applications and documents. Additionally, the requirement for user permission to install is not a characteristic of a virus, as many viruses operate covertly, spreading without explicit consent from the user.