What is a botnet in the context of security?

A botnet refers to a collection of compromised computers that are controlled remotely by an attacker, often without the knowledge of the device owners. These compromised machines, often referred to as "bots" or "zombies," are typically infiltrated through malware infections. Once a computer is part of a botnet, it can be used for various malicious purposes, such as launching distributed denial-of-service (DDoS) attacks, sending spam emails, or stealing sensitive information.

The focus of a botnet is on the exploitation of multiple devices to serve the attacker's goals, making it a notable concern in cybersecurity due to the scale and difficulty of detection. The other options do not accurately capture the malicious nature and structure of a botnet. For example, a network of secure servers would imply a safe and well-managed environment, which is the opposite of a botnet made up of compromised systems. Similarly, an encryption algorithm and vulnerability detection software relate to security measures, rather than the concept of a compromised network used for nefarious purposes.