Which term describes the technique of controlling previously compromised systems to conduct illegal activities?

The term that describes the technique of controlling previously compromised systems to conduct illegal activities is "botnet." A botnet refers to a network of infected computers, often referred to as "zombies," which are controlled by an attacker without the consent of the owners. The attacker can leverage this network to perform various malicious activities, such as sending spam emails, conducting distributed denial-of-service (DDoS) attacks, or mining cryptocurrency.

In this context, "botnet" accurately captures the idea of a collection of compromised systems being directed as a group to achieve malicious objectives. Systems in a botnet are typically infected with malware that allows the attacker to maintain control over them, enabling a wide range of exploitative functions.

Other terms, while related to cybersecurity, do not fully encapsulate the organized control and utilization of compromised devices in the same way as a botnet does. Exploited networks, for example, could refer to any network that has been breached but doesn't imply the organized control aspect associated with botnets. Backdoor access refers more to a method of bypassing security controls on a single system rather than controlling a network of systems. Malware infrastructure, while related to the tools and frameworks used for malware deployment, does not specify the network aspect