Command and control server

A botnet is a number of Internet-connected devices, each of which is running one or more bots. Botnets can be used to perform distributed denial-of-service attack (DDoS attack), steal data, send spam, and allow the attacker access to the device and its connection. The owner can control the botnet using command and control (C&C) software. The word "botnet" is a combination of the words "robot" and "network". The term is usually used with a negative or malicious connotation.

A botnet is a logical collection of internet connected devices such computers, smartphones or IoT devices whose security has been breached and control ceded to a third party. Each such compromised device, known as a "bot", is created when a device is penetrated by software from a malware (malicious software) distribution. The controller of a botnet is able to direct the activities of these compromised computers through communication channels formed by standards-based such as IRC and (HTTP).

Botnets are increasingly rented out by cyber criminals as commodities for a variety of purposes.

Botnet architecture has evolved over time in an effort to evade detection and disruption. Traditionally, bot programs are constructed as clients which communicate via existing servers. This allows the bot herder (the person controlling the botnet) to perform all control from a remote location, which obfuscates their traffic. Many recent botnets now rely on existing peer-to-peer networks to communicate. These P2P bot programs perform the same actions as the client-server model, but they do not require a central server to communicate.

The first botnets on the internet used a client-server model to accomplish their tasks. Typically, these botnets operate through Internet Relay Chat networks, domains, or websites. Infected clients access a predetermined location and await incoming commands from the server. The bot herder sends commands to the server, which relays them to the clients. Clients execute the commands and report their results back to the bot herder.

In the case of IRC botnets, infected clients connect to an infected IRC server and join a channel pre-designated for C&C by the bot herder. The bot herder sends commands to the channel via the IRC server. Each client retrieves the commands and executes them. Clients send messages back to the IRC channel with the results of their actions.

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Wikipedia