For those of you who either aren't tech-savvy or have been led by CSI to believe that DDoS stands for "Dangerous DOS Office Spam," a distributed denial of service attack floods a server with so many simultaneous requests that it slows to a crawl and can't do anything. It's like shutting down a sandwich shop by sending in 300 people to all demand their order at once. Only in this case, it was up to 600,000 computers that had been linked into a botnet through malware infections.
That botnet, called Mirai (after an anime, because people launching DDoS attacks to gain an advantage in Minecraft are, shockingly, kind of nerdy) was built by three students to take down both rival servers and tools specifically designed to stop DDoSes. Once they realized how powerful Mirai was, they decided to see what else they could do with it. One of them repeatedly crashed his college's network, and they also started targeting organizations and either extorted them to call off the attack or offered a "service" to protect them.
Eventually they made their code open-source in an effort to muddle attempts to track them down. That led to 2016's Dyn attack. Dyn's perpetrators are still unknown, but they killed internet connections all along the East Coast, bringing major services like Netflix and PayPal to a standstill. It was a day that will live in infamy because we were all forced to converse with each other in person. All these shenanigans attracted the attention of the FBI, and Mirai's creators were eventually caught. We guess the lesson for all you kids out there is this: Don't try to turn your sketchy Minecraft cheating into a criminal empire.