Remote Access To Computer Through Wireless Network

I suspect that he did something and gained remote access to my computer.I found out about it when I checked my wireless connections on my router and found his name on the network : Steve's - Iphone and a couple of unfamiliar connections. I then opened my task manager and ended some tasks I thought were possibly infected. When I went back to the wireless status, the unfamiliar connections disappeared.

I use Norton firewall + kaspersky internet security and my virus definitions have always been up to date, but I cannot detect anything. I also set my options to permit only MAC authenticated computers and changed my wireless WPA/WPA2 key, but every time I turn my wireless on, this guy somehow is connected to my network. [code]