What characterizes a computer virus?

A computer virus is characterized primarily by its ability to replicate itself and execute specific actions when certain conditions are met, often referred to as "activation goals." This behavior is a fundamental aspect of what defines a virus, as it is designed to spread from one system to another, potentially causing damage or unwanted behavior upon execution.

Viruses often require a host file to infect and can remain dormant until their activation conditions are triggered. This could involve a user opening a specific file, or the virus being executed during certain system conditions. Understanding this replication mechanism is crucial when studying computer security, as it highlights the ways in which malware can propagate within networks and systems.

The other choices do not correctly define a computer virus. Encryption and decryption mechanisms are closely related to data security but do not inherently relate to replication or the malicious intent of a virus. Tools that enhance network performance address optimization rather than malicious replication, and firewalls are aimed at securing networks by preventing unauthorized access rather than being a characteristic of a virus itself.