How did I get hacked?

I logged in today after not playing for like, a year, to give a friend an item, and all my stuff is gone. I don't really care about the stuff, because I don't plan on playing MapleStory anymore, but I'm curious as to how my account security was compromised without me so much as visiting a MapleStory-related website besides this forum. I changed my password regularly before I quit, it wasn't something easy to guess, and no one had my account info. Can anyone offer an explanation?

Chances are one of the many security derps Maple has had which allows people to get your info.

This here thread has most of the know info about the hackings.