Which of the following is classified as "malware"?

Malware, short for malicious software, encompasses a variety of harmful programs designed to infiltrate, damage, or disable computers and networks. Viruses fall under the category of malware as they are specifically designed to replicate and spread, often causing harm to the infected machines.

In contrast, firewalls serve as a security measure to protect networks by monitoring and controlling incoming and outgoing network traffic based on predetermined security rules. Routers function to direct data packets between different networks, facilitating communication but not inherently introducing malicious behavior. Encryption is a technique used to secure data by converting it into a coded format, ensuring confidentiality and integrity, but it is not malicious in nature.

Thus, viruses are classified as malware due to their intended purpose of causing harm and disruption, making the identification of viruses as malware accurate in this context.