A botnet, i.e. a bot network (also known as a zombie army) is a network made up of a large number of computers that have been hijacked by malware to serve the whims of the hacker who unleashed it. By taking control of hundreds or thousands of computers, botnets are typically used to send out spam or viruses, steal personal data, or to stage DDoS attacks. They’re considered one of the biggest online threats today.
For your computer to be part of a botnet, it first needs to become infected with a type of malware that either contacts a remote server, or other infected computers in the network, in order to get instructions from whoever is controlling the botnet, which is typically hackers and criminals. Despite being grander in scope and scale, however, a botnet malware infection is no different from a typical malware infection.
You can recognize a computer infected with a botnet in much in the same way as you can identify a computer infected with other types of malware. Signs include the computer I running slowly, acting strangely, giving error messages or the fan starting up suddenly when the computer is idle. These are all possible symptoms of someone using your computer remotely as part of a bot network.
To remove a PC from a botnet network, you need to remove the malicious software that’s controlling it. The best way to do this is to run an antivirus scan of your computer, which should locate the botnet malware, then remove it for you - an easy solution to a dire problem.