What do I do with a hacker on my AIM?

I have changed my password already but I don't know how they would have gotten my password in the first place. They know my friends' names because the hacker comments on statuses and when they do they say mean things about my friends. They obviously don't like me because they pried a secret out of my friend and then told my bff the secret and now they both hate me! I already changed my password but I didn't tell ANYONE my password. I am afraid they might do it again.