How do hacking softwares work?

[Little boxes]

This person hacked my facebook the other day, and to prove it, he sent me bits of the conversation that I had with my friend on my ask.fm. He keeps telling me that changing the password won't help because he's got some hacking software. Currently, he doesn't have access to my account.
But I still need help. What can I do to make sure no one besides me can access my account? Please help.
He's anonymous whenever he posts on my ask.fm.

[Merryquiet107]

Aren't you a, cute, gullible child. Change your password. Trust me, there's nothing he can do.

[dom]

There are available many Hacking software in Online Market but only one software work properly. Hacking software try to to find out hash of your id and then Decrypt the hash and show your password.

[Ali]

Hi,dear.I believe teaching and using this illegal means is immoral and illegal!?You may sue that person,block him,and notify your carrier!?Breaking privacy rules!?