DDOS? Who would order DDOS against an ICANN accredited registrar and for what purpose? Some competing registrar is the only possible candidate I can think of...
In any case, Dynadot must fix their systems globally and ASAP. With or without anti-DDOS solutions, they have a lot to fix. Not only frequent "planned" shutdowns. As noted in other threads, their BIN sales landers were not working in December (a few days!): "Add to cart" button did not add the domain to a shopping cart. Also, in August or September their domain forwarding stopped working (a few days to fix). The last but not the least, in early January dynadot dns was not updating for hours... updates were received but not applied to real dns responses. And, yeah, "our engineers are working on it". Such a low stability is not something one expects from a winner of Namepros Top/Fav. registrar polls...