I just discovered someone was using my wifi, that I opened for a friend who was having a problem with WPA. I don't want to be malicious to him, but I want to send him a message about what he's doing, and maybe see if he wants to keep using my bandwidth (maybe for a fee). Is there any way on my macs to get his email address or AIM or something. Like a Man in the Middle attack, but only using osx? Or some other way to track him down?