What are the different types of hacks?

So my friend has been getting hack in his game and where trying to figure out how he did it so we can stop it. He just recently built a computer and yet the hacking still occurred. we've tried a bunch of different security's but they do nothing. He hasn't opened and spam of anything like that either. So what could be causing this? One person does know the password and they say there account is being hacked also. If you need to know the game is Runescape. please let me know how you think he's being hacked and a way to stop it. thanks you very much :)