What is a botnet?

A botnet is accurately defined as a collection of compromised computers that are controlled by a single entity, often referred to as a master node or botmaster. These compromised machines, known as bots or zombies, can be used to perform malicious activities such as launching Distributed Denial of Service (DDoS) attacks, sending spam emails, or stealing information without the knowledge of their owners.

The term "botnet" emphasizes the network aspect, where multiple infected devices communicate with each other and follow commands from the master node. This large-scale coordination significantly amplifies the potential for harm, as a botnet can harness the power of thousands of computers to execute tasks simultaneously.

In contrast, the other options do not accurately define what a botnet is. While a network of unauthorized users may exist, it does not capture the specific concept of compromised machines being controlled for malicious purposes. The definition involving malware that spreads via email is more aligned with typical behavior of viruses or worms, but it does not encompass the broader functionality and structure of a botnet. Lastly, software designed for data encryption relates to data security and integrity but has no connection to the concept of a botnet or its functions.