Although not malware themselves and originally even designed to be helpful, botnets are currently considered the biggest threat on the internet.
By definition a botnet is a herd of slave computers, often referred to as zombies, that are under control of a botnet operator that runs or controls the C&C (command and control) server(s). Botnets are being used for multiple tasks including: denial-of-service attacks ( DDOS ) , spreading spam, bitcoin mining, clickfraud and stealing personal and financial information. They also distribute malware, including the kind that can turn your computer into a zombie in order to make the botnet grow.
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