Werewolf Invasion is a quest in The Elder Scrolls Online
You have to fend off a Werewolf invasion.
Kill all Werewolves in the area to complete the quest.
UPDATE || 4/3/2014 Confirmed there is no Werewolf Invasion quest in Mournhold. Furthermore most sources have no solid answer as to where there are any werewolves. They are a rare spawn at night only in high level zones. No further information at this time.