Site5 relies on DYN, the company that was the main target of the attacks. Thus their own DNS servers were attacked as well.
It doesn't help using functional DNS servers, like the OpenDNS servers, when they on occasion have to refresh their DNS info from servers impacted by the attacks. At present, NG has apparently lost its DNS records and is in effect orphaned in cyberspace. Only by making a direct pointer to its IP (through the HOSTS file) outside ordinary name resolution can we access the site.
I agree hard-coding HOSTS isn't a solution for all eternity, but it's the only feasible approach right now until Site5 gets their act together.
When everything is back to normal, open your HOSTS file and add a comment sign (#) first on the line for NG. That's all.