How did the Mirai DDoS Botnet infect 600,000 + IoT devices and lead to an explosion in Mirai Variants?

Here is the outline: Outline of my Project

Title:How did the Mirai DDoS Botnet infect 600,000 + IoT devices and lead to an explosion in Mirai Variants?

Questions: What was Mirai? What are the main targets for Mirai? How was it deployed and propagated in initial creation? How were so many variants of Mirai created after release? How was Mirai detected? What protection (if any) was in place that failed? What was the impact of the attack on victim’s of Mirai? What was the impact on Business? How could an attach like this be prevented now? How could an attack like this be prevented in future?