What does the term botnet refer to?

The term "botnet" refers to a large automated and distributed network of compromised computers. In this context, a botnet is created when a collection of infected devices, often referred to as "bots" or "zombies," is controlled remotely by an attacker. These devices can be used to perform various malicious activities without the owners' consent, such as sending spam emails, launching distributed denial-of-service (DDoS) attacks, or stealing personal information.

The defining characteristic of a botnet is its decentralized nature, where each compromised device contributes to the network's overall power, enabling coordinated actions across many machines. This ability to harness the processing power of multiple computers makes botnets particularly powerful for attackers. They can grow in size as more devices become infected, which often happens without the knowledge of the device owners, further complicating detection and mitigation efforts.

In contrast, the other options describe different types of technologies or concepts that do not relate to the malicious context of a botnet. For example, a network solely used for data backup pertains to storage solutions, a secure virtual private network relates to encrypted communications, and a firewall focuses on protecting against unauthorized access and certain types of attacks rather than being a network of compromised machines.