  As item trading becomes more popular, users can change their game items or
money into real money more easily. At the same time, hackers turn their eyes on
stealing other users game items or money because it is much easier to earn
money than traditional gold-farming by running game bots. Game companies
provide various security measures to block account- theft attempts, but many
security measures on the user-side are disregarded by users because of lack of
usability. In this study, we propose a server-side account theft detection
system base on action sequence analysis to protect game users from malicious
hackers. We tested this system in the real Massively Multiplayer Online Role
Playing Game (MMORPG). By analyzing users full game play log, our system can
find the particular action sequences of hackers with high accuracy. Also, we
can trace where the victim accounts stolen money goes.
