Confusion on game servers

[78]

So for an online game, when a game server is active and has everything saved online, there could be database breaches in order to hack and get control of a lot of accounts and passwords. But if the databases are stored locally, somewhere only the developing company knows, and it is an online game requiring internet as a must to play, is it even possible to take down the server and claim the databases. If so what are the methods that could be used to hack it and what the techniques which could be implemented to prevent an attack?

Actually, what are techniques to hack into a game and unlock the full potential for all the platform including modding? How do they really work using modern technologies that are available?

[6]

If it's an online game that's halfway decent (many aren't) it'll have server-side verification so nothing a player does could go out of the bounds of what's intended.