I have never been hacked but if you have been hacked, What you should do is this,
Change you password like superboyian did.
Stop using third party applications on Facebook like Farmville, Mafia Wars, Social Interview, etc They are not regulated by Facebook so people can hack into them and steal information from users using them. I understand they can be fun and addicting but try your best to avoid them.
Don't Click on links from friend in a message like "Hey, I saw you in this video, I can't believe this you got to see it, etc" If the link looks suspicious with numbers (53.533.932 or any other variation of that) or another site you never herd of, Don't follow it.
I have noticed that new fan pages are forcing you to go to an outside site and take surveys to see the content. Don't do the survey that some pages forces you to do them, someone might hack them or deliver the info directly to a hacker. Not to mention the surveys might also force you to give a cell phone number, which enrolls you in a dumb subscription service or something and might open the door to new spam and such
Im sure if you follow these you shouldn't encounter much more in the future. Hope this helps
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My AS has its Up and Downs, But I think that it's for the better. The world would be a less interesting place without me and my AS.