Does anyone have a simple explanation or link to an article / blog that explains the naked domain / ALIAS "problem" that DNSSimple solves? I recently set up DNS with DNSimple (due to nudging by Heroku) and am affected by this DDoS. I am still struggling to understand the exact nature of this issue. All of Heroku's documentation is pretty cryptic (to me):

"Some DNS hosts provide a way to get CNAME-like functionality at the zone apex using a custom record type. " .. and then on to suggest DNSimple as their first suggestion.