Which of the following is an example of malware?

Malware, short for malicious software, refers to various types of software designed to harm, exploit, or otherwise compromise computer systems and networks. A virus is a specific type of malware that replicates itself and spreads to other programs or files, often leading to damaging effects such as corrupting files, stealing data, or using system resources without the user's consent. By categorizing a virus as malware, it aligns perfectly with the definition of harmful software intended to disrupt normal computer operations.

In contrast, a firewall is a security system designed to monitor and control incoming and outgoing network traffic based on predetermined security rules, thus serving a protective function rather than being harmful. An email filter helps manage incoming messages, detecting spam or phishing attempts, which also doesn't fall under the malware classification. A web browser is a software application used for accessing information on the internet; like the previous two options, it is not designed to cause harm but rather to facilitate web navigation and access. Therefore, the virus is the clear example of malware among the given choices.