What is the term for a singular compromised system that can be instructed to perform tasks and attacks?

The term for a singular compromised system that can be instructed to perform tasks and attacks is known as a "bot." A bot is typically a device or system that has been infected by a piece of malware, allowing an attacker to control it remotely. This can include performing tasks such as sending spam, participating in distributed denial-of-service (DDoS) attacks, or other malicious activities without the owner's knowledge.

The nature of a bot allows it to operate under the direction of an attacker, often as part of a larger network of compromised devices referred to as a "botnet." This capability distinguishes it from other types of malware, as bots are specifically designed to automate tasks for the attacker, making them powerful tools in cyber operations.

In contrast, the other options represent different concepts within cybersecurity. An "agent" usually refers to a piece of software that acts on behalf of a user or system but doesn’t inherently imply compromise or malicious intent. A "Trojan" is a type of malware that tricks users into executing it by masquerading as legitimate software. A "virus" is a self-replicating malware that requires user action to spread and infect other systems. Understanding the functionality and potential of a bot offers insight into how attackers can exploit compromised systems