Hijacked Wireless Network?

A user, peteliot, wrote into the Netsecurity Forums with a question regarding wireless network security and attempting to determine if a rogue wireless device had connected to his network or if some attacker may have hijacked his wireless network:

...There are only 2 computers on this network. Today my computer sounded the notice that someone had signed in. I checked my wife's computer and it was off. My wireless network is supposed to be firewalled and there are no other authorized users. My question is, how do I configure my computer to show me who is signed into the network?...

To see my reply to this thread or help out with some of your own insight or advice, visit this thread in the Netsecurity Forums.