Injectors

I'm kind of new to hacking and programming and I am a bit confused by the idea of injectors. I have read that hacking server sided games isn't possible without hacking into the game's actual servers which you can be arrested for. So, I was wondering if injectors a basically a bypass for this because I always thought Combat Arms was a server-sided game but people use injectors for it all the time. Or is Combat Arms client-sided and you can only use injectors for client-sided games? Thanks for any help.

Injectors simply inject .dll's into the Game Process, which then are used for hacking possibilities. The game simply reads the code in the .dll and executes it. Nothing server-sided about it, it's all on the user's end.