Minecraft.net's session servers are currently being DDoSed. Until the hackers stop/Mojang find a way to kill stop them, then sadly there's nothing EMC staff/you can do to fix it. It affects everyone - it's not just limited to EMC. :/
The Minecraft session and login servers have been down for about 2-3 hours. We're all going through this at the moment - every single Minecraft player in the world.
The session servers are being DDoS'd. Quite a rudimentary way of trying to take it down... I quote Daniel Frisk: "DDoS is for losers who can't hack properly"
Smart? They're idiots. You can figure out how to DDoS a website in a few minutes or maybe hours. Just find a vulnerable port and overload it. It's not even very effective. You shut down the program you're using to DDoS, you stop DDoS'ing that site and by the time you've loaded it up again, you will have to wait awhile to find that port. By the time you find it... Well, you won't be able to DDoS it anymore.
All we have to do is wait for them to take a little nappy and have their mommy tuck them in and we can play minecraft again.
DDoS is for people for who can't hack. It's like this; "I can't stealthily pick the lock on that door, so I'm going to repeatedly throw a rock at it until I get in".