What defines a botnet?

A botnet is specifically defined as a network of infected devices that are controlled by a central entity. This central control typically enables the attacker to manage the devices remotely, often without the knowledge of the device owners. The infected devices, commonly referred to as bots or zombies, can be used to perform various malicious activities, including distributed denial-of-service (DDoS) attacks, sending spam emails, or stealing personal data.

The central characteristic of a botnet is its controlled and coordinated operation by the attacker, which allows for a significant scale of malicious activity by leveraging the resources of many compromised devices. These devices can range from personal computers to IoT gadgets, all functioning under the control of malware that has infected them.

While the other options mention networks of devices, they do not capture the key elements of a botnet, such as the infection of devices or the central control aspect. A botnet is not characterized as a secure network, a decentralized network, or solely a communication network, as these definitions miss the critical point of compromised devices being leveraged for harmful activities.