A botnet is a network of internet-connected devices, such as computers, smartphones, or Internet of Things (IoT) devices, that have been infected with malware and are under the control of a single attacking party known as the "bot-herder". Each infected device, known as a "bot," is created when a device is penetrated by software from a malware distribution. The bot-herder can control the botnet using command and control (C&C) software, and the bots serve as a tool to automate mass attacks, such as data theft, server crashing, and malware distribution. Botnets can be used to perform Distributed Denial-of-Service (DDoS) attacks, steal data, send spam, and allow the attacker to access the device and its connection.

Botnets are usually created when the bot-herder sends the bot from their command and control servers to an unknowing recipient using file sharing, email, or social media application protocols or other bots as an intermediary. Once the recipient opens the malicious file on their computer, the bot reports back to command and control where the bot-herder can dictate commands to infected computers. Botnet infections are usually spread through exploiting security issues in software or websites, delivering the malware through emails and other online messages, or tricking the user into running a Trojan horse program.

Botnets are highly illegal, and operating one is a serious cybercrime. They are a significant cybersecurity concern to governments, enterprises, and individuals. To protect against botnets, it is recommended to use anti-virus software that detects malware, remove what’s on your device, and prevent scammers from installing them on your computer, tablet, and phone.