So me and my roommates decided to have a small in-house security competition. The rules were simple: break in, create a new directory containing a small .txt file and exit. We also agreed to full disclosure after it was all over. Neither one of us claim to be security experts, it was all fun and games. Anyway, I won the first round . I managed to compromise both of my victims security settings and consequently win some free beer. However, wanting revenge, my roommates wanted a rematch. We got one week to improve our defenses before round 2 took place. This time around one of my roommates got wise and managed to fool me . He changed some settings in his registry (XP.) The settings he changed makes him completely invisible to the outside world! I tried Nmap, Nessus, LanGuard, nothing! No trace of him existing! How is this possible? Is there any way besides using a scanner to flush him out? I would greatly appreciate if someone could explain this to me (Yes, I've tried to Google for it.) Round 3 is around the corner and it would be nice to reclaim my crown of in-house uber haxor . We're all on XP/nix dual-boot boxes.