I remember an infamous group on Xbox 360 who ran round DDOSing people during Halo 3 matches. Host Got Booted they were called. They were a huge problem.
I had the fun of being host when I ended up matched with them. They tried to DDOS me. My ISP realised what was going on that some weird other IP had started sending data at me without any reason and they re-routed the packets back at them. 30 seconds of lag my end before it returned to normal and I got to hear the sound of Host Got Booted DDOS attacking themself. I do wonder what happened because the last word I heard over voice chat were "The routers is on fire, **** **** **** the router is on fire. Use the curtains to beat the flames....................... **** the curtain are now on fire too unplugs it all!!!!"