I assume that it must be related to Nidhögg, the dragon who eats the root of Yggdrasil (http://en.wikipedia.org/wiki/Níðhöggr), although I can't find anything in Wikipedia that would confirm this. If the dragon symbolises the forces of chaos steadily working to destroy the tree of life, and his finishing the task heralds Ragnarök; and if nidingsdåd, the evil acts of nithings, are his acts, then the evil force possessing/motivating their magic as mentioned in that fascinating encyclopedia article has very serious connotations indeed. The fundamental chaos/evil working to bring about the end of all life... yeah, it's clear the past connotations at least, if not the more recent/widely-known ones, are pretty severe.