Please help. Weird things happening on facebook?

[Victoria]

I made some friends from my school. Since, I started hanging out with them, alot of things going on. FACEBOOK. Someone went to my friends account. He/she read ALL the messages I sent her. It's personal. Next day, a girl added me. I never heard of her. Let's call her Ariana. I asked on Facebook if we met before. She said, No bitch I'm a hacker.
"I'm the one who read your friend's messages. I know everything"
I said "Shut up you lying c*nt you know 13 year old can't hack a damn facebook. Or you know her password". (Sorry for bad languages)
Anyway, she added almost the half of my friends on facebook. She's also messaging them. If I block her she said "If u gonna block me imma hack u too" What the hell? HAHAHAHA!!! Do you find this funny or just WTF?

[Hennymaster]

You can easily get rid of her. First change your password and check "Log me out other devices I logged in to" then Facebook will log you out if you had logged in to another device and incase your password was stored or saved on the browser. Second also change your email address. Don't save your password on the browser. like Google Chrome and Mozilla Firefox will ask you if you want to save your password, Just choose no.

[an !dea]

Prank! Is what I'd call this.

One of your friend is fooling you with a fake account. If you don't wanna block that id then put it in restricted group, and (as hennymas said) change your password. ALSO, ADVICE YOUR FRIENDS not to let their id be used by others and ask 'em to change their password.