DDoS attacks are super hard to mitigate whenever it comes to video game environments. They don't have the same capability as a CDN does (your Netflix, Amazon, Cloudflare, Akamai). So they suffer a bit harder than other groups. And as Enkidou said, terms of service cover them in this capacity. They can't prevent acts of god or people from doing bad things. Even so, I do not care for NTT. Their infrastructure is terrible in San Jose.