Final answer:
option a,A botnet is a network of compromised computers controlled by a hacker used for malicious activities.
Step-by-step explanation:
A group of compromised computers controlled by a hacker is called a botnet. A botnet is a network of private computers infected with malicious software and controlled as a group without the owners' knowledge, usually for criminal purposes such as sending spam or conducting Distributed Denial of Service (DDoS) attacks. The hacker can command these 'bot' computers remotely, which makes botnets a significant threat in cybersecurity.
A group of compromised computers controlled by a hacker is called a Botnet. A botnet is a network of computers infected with malware that allows the hacker to control them remotely. The hacker can use the botnet to carry out malicious activities like launching DDoS attacks, sending spam emails, or stealing sensitive information.