What is a botnet?
A botnet is a network of infected computers that are all remotely controlled by someone else. Botnets are used for various criminal activities, all of which can seriously affect your computer.
Once your computer is under the control of a botnet, adware and spyware may be added to it. A computer controlled by a botnet may also be used to send out spam emails, host phishing sites or infect and attack other computers.
A computer can become part of a botnet when it's infected by a virus, Trojan or worm. If your internet connection is unusually slow when you're online, this may be a sign that it has been infected.