Twice in the last six months an unknown computer has shown up on our home network. We had a machine running ME that may have been hacked in some fashion, plus 3 XP boxes. What might have allowed them to actually set themselves up on our network (behind a router/firewall and zonealarm (may have been inactivated on the ME box). If the network is cleaned up now what would it take for someone to set themselves up again and how can I secure against this.