We will never ask for your password
The common use for this is for someone to get access to another persons game account and then sell any items on it. This is often done towards the players computer or with social hacking but the players will still blame the developer. So there need to be a way to track changes and to recover lost items. One also needs to educate the players in what to watch out for when someone is trying to steal their account.
Passwords and Reuse
Bots are programs that play your game.
Someone manage to copy some parts or the whole of one or more databases.
A denial-of-service (DoS) attack (https://en.wikipedia.org/wiki/Denial-of-service_attack) is when someone try to interrupt or suspend your games connection to the internet.