The authentication servers at Mojang are down for the moment, so you can’t login and play on any Minecraft server. Hope they will solve their problems soon.

A quote from Daniel Frisk’s Twitter, chief arhitect at Mojang:

There seems to be some kind of attack on our servers. DDoS is for losers who can’t hack properly.

Source: https://twitter.com/danfrisk/status/269883097317769216

Oh the irony… Should I feel humbled that we seem high profile enough that DDOS kiddies attacked us mere minutes before Mojang, or sad that said kiddies have no life?