How to Spot a Botnet
Most cyberattacks don’t come from a single hacker sitting behind one computer. Instead, they rely on thousands of devices working together without their owners’ knowledge or consent. These networks are called botnets, and they’ve become one of the most powerful tools in modern cybercriminal arsenals.
A botnet is a network of computers or Internet-connected devices (IoT) infected with malware, allowing an attacker to control them remotely. Attackers can use a variety of methods to infect devices, from exploiting unpatched vulnerabilities and guessing weak or default passwords to phishing and malicious downloads. Once a device is infected, it will reach out to a command-and-control (C&C) server for instructions. This enables the attacker, or ‘bot-herder’ to amass large networks — sometimes containing millions of zombie computers – which they can use for their malicious purposes.
C&C servers can be centralized, with each device connecting to the server individually; or decentralized through peer-to-peer (P2P) systems, where the infected machines act as both clients and servers. Either way, bots are programmed to communicate with the C&C using the same methods as normal devices, making it difficult for defenders to detect them.
To identify a botnet, security teams need to move beyond blocking specific IP addresses and looking for common signals: reused leaked credentials or card data, consistent device fingerprints, matching timing patterns, or coordinated downstream behavior. Regular updates to software and IoT devices can help prevent exploitation, but the best way to spot a botnet is with real-time monitoring that looks for these indicators and includes threat intelligence and behavioral analytics.