What is Botnet?A botnet is a collection of infected systems that are controlled by an attacker
A botnet is a collection of infected systems that are controlled by an attacker. Typically systems are joined automatically, by abusing common weaknesses (vulnerabilities) in software.
When the attacker manages to break into a system, a little program is activated to join the botnet. From that moment, this new system is considered to be a 'zombie'. The attacker can remotely give all zombies a particular task to complete. Such task might be sending spam emails, attacking other targets, or overwhelm websites with dummy requests.