Would someone have to know my password to hack into my facebook account?

[Sarah]

I just asked a privacy setting question on here (because apparantly my privacy settings had somehow been changed so that everyone could view my profile, and it wasnt me) and someone said that someone must have hacked into my facebook account. But I dont know how they could have. I was 8 numbers as my password, and I dont log in when anyone else is around. Plus I have my own computer, and know for a fact that know on goes on the internet on it. So it couldnt be that I was still logged in and someone went on it. So is it possible that facebook changed my settings somehow? Plus if someone had hacked into my account, why would they just change my privacy settings, and nothing else? Btw, I did already change my password.