AIM, anyoneknow how to block or prevent strangers from stalking you?

[FrenchTV]

I just checked out AIM on the ipad, seems cool, reliable but.... even after i close it i get messages in the middle of the night from people i dont even know, is there any way to prevent people you DONT KNOW from finding your AIM ID and stalking you, like only allow people in your AIM friends list to contact you, even when im Invisible i get messages