How do hackers create a botnet?

Hackers create a botnet primarily by taking control of multiple computers, often without the knowledge of the computer owners, to form a network of compromised machines, commonly referred to as "zombie" PCs. These zombies are connected to a master computer or command-and-control server which allows the hacker to remotely manipulate the infected machines to perform various malicious activities, such as sending spam, launching distributed denial-of-service (DDoS) attacks, or stealing sensitive data.

The method involves the deployment of malware, such as Trojans or worms, that exploits vulnerabilities in the target computers. Once the malware successfully infects a machine, it communicates back to the hacker's server and waits for commands, thus creating an extensive network of controlled devices.

This answer highlights the fundamental principle of how botnets operate—by transforming ordinary computers into malicious tools under the hacker's control, allowing for coordinated and large-scale attacks using the collective power of these "zombie" PCs.