Which of the following is commonly used in a distributed denial-of-service (DDoS) attack?

Botnets are often used to launch DDoS attacks, with the attack coming from all the computers in the botnet simultaneously. Phishing attacks attempt to get the user to give up information, click on a link, or open an attachment. Adware consists of unwanted pop-up ads. A Trojan horse attaches malware to a legitimate program.