Botnet malware is specifically created to allow control over a computer to make it work as a member of a botnet. A botnet is a large collection of bots that is used to perform nefarious tasks in unison.
Botnets are most commonly used for sending spam, stealing sensitive personal and financial information, denial of service attacks and expanding the botnet itself. Botnets provide their controllers with a vast amount of computing power and make it harder for them to be caught.
Any type of malware can be used to turn a computer into a bot. By using an up-to-date virus scanner, setting up a firewall and being aware of the websites visited, users can protect their computers from malware.