Botnet

A botnet is a network of compromised computers (bots or zombies) controlled remotely by an attacker. Infected computers — which can include servers, desktops, IoT devices, and even phones — receive commands from a central control server and carry out coordinated malicious activities like DDoS attacks, spam campaigns, or credential stuffing attacks.

Your systems can become part of a botnet without your knowledge if they're infected with bot malware. The bot software runs quietly in the background, waiting for commands from the attacker while using your systems' resources and network bandwidth for malicious purposes.