I've suddenly gotten curious about those messages that are shown when a player leaves the game. I am wondering about three of them:
1 - "Socket Error: Read Error",
2 - "Connection Closed"
and 3 - something about "due to quitting".

When is 1 shown, and what's the difference between 2 and 3?

2 = Someone disconnecting via external methods (e.g. Alt + F4)
3 = Someone disconnecting (quitting) through the game-menu