An invulnerability found in the depths of OpenSSL. It can be used to leak information including usernames, passwords, addresses, credit card and/or paypal information, etc.
As stated by Mojang, their servers were not affected but the load balancers they use from Amazon were affected and it's possible some information has been leaked. I strongly suggest you update your account information and change your password for security sake. For more information reguarding the current status of Mojang and their experience regarding the problem can be found below.