Answer:
D) denial-of-service
Explanation:
These computers are used to execute denial-of-service attacks. These attacks force all of the infected devices to enter a certain companies' website which ultimately overwhelms their servers and causes their entire service to crash. Hackers do this for a wide range of reasons but most of the time it is done in order to create vulnerabilities in the companies security so that they can exploit these vulnerabilities and gain access to sensitive data.