Yesterday on two occasions I saw on the "Shared" list in the finder a computer appear! It was just listed as its MAC address. First time I've seen this happen, It wasn't the MAC address of my iMac, (or my iPhone, though that wasn't on the network at the time anyway. I opened up airport utility and there was nothing I could see logged on to the wireless network (with WPA2 security) I tried open (click) on the shared device and it was disallowed as I didn't have the privileges. Info just said it was a PC, then it logged itself off. My current setup is: ADSL modem/router connected to internet and acting as NAT, supposedly with hardware firewall on. A Time Machine connected to the ADSL, in bridge mode, with the wireless network (with WPA2 security, I never bothered to turn on specific MAC access.) I'm careful, I think, about what I install, and don't thing I've installed a Trojan, though could this do this?