iChat hacking warnings from iChat?

Hi. I was away from my computer for a day and when I returned I had an IM from a Screen Name that has been harassing me for a couple of months. They keep trying to video chat me or IM me, but I never answer. When I returned to my computer this morning, there was an IM that I opened and was finally going to say something to the person, but when I opened it, there was a couple of messages saying that they have downloaded all of my information and passwords and files. I am going to attach a photo so you can see. It looks a little fishy. I called Apple and they have never seen it. There are no articles about anything like it on google. The persons SN is bolded which is odd since usually when iChat tells you if someone has signed off or on, the SN is not in bold. Also iChat never gives warning messages like these. I feel like it is some script for iChat that someone started using. If not and someone has in fact hacked my system, which I don't believe someone can do through iChat, can someone let me know what to do. Also if they hacked my system some other way, I don't see why iChat would warn me about it and not something else in the computer. Thanks!