Blizzard Customer Service is in the process of dealing with connection issues facing players on both sides of the Atlantic Ocean. For the North American players, login errors have been plaguing both the Account Management website, and several games--World of Warcraft, Diablo III, and Hearthstone.
For players in Europe, Blizzard noted yesterday on their EU support blog that the high latency and connection issues are, in fact, the result of a series of DDoS attacks that have been levied at Blizzard servers for the past few days. Blizzard is monitoring the situation and asks that players follow their European customer service Twitter account for updates and further information.
(NA) We continue to look into the login issues for the website (Account Management, forums, etc) & in game. WoW - Error 113 D3/HS - Error 73- BlizzardCS (@BlizzardCS) April 1, 2014