Botnets are a herd of slave computers, often referred to as zombies, that are under control of a botnet operator. They are being used for multiple tasks including: denial-of-service attacks ( DDOS ), spreading spam, bitcoin mining, clickfraud and stealing personal and financial information. Most botnets are for hire, which means if you have enough bitcoins and know where to find them maybe you can hire them. Botnets currently considered the biggest threat on the internet. They also distribute malware that can turn your computer into a zombie in order to make the botnet grow.”]
Source: https://blog.malwarebytes.com/cybercrime/2015/02/the-facts-about-botnets/