Basicaly, i have no idea what happened. my guess is that somthing got hacked. i keep getting random chat messages on singleplayer from rockandroll (or somthing like that) and this other person. the weird thing is, is that my internet was screwed up at the time, and i have no idea what happened. (i had optifine HDU E1 installed)
Can this be reproduced in vanilla minecraft? If so,
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report (
[minecraft|http://hopper.minecraft.net/help/finding-minecraft-data-folder]/crash-reports/crash-<DATE>-client.txt
) here.