We spend so much time worrying about wireless networking we forget to also consider what might be attached to the wired network. What is hidden behind the wall?
Actually I built a network tap for administrative purposes, but it shows how easily something like this could be hidden in the wall behind the sheetrock. Does not hurt to pull the screws once in a while to see what is there.
Connected to the passive tap also could be a wireless device which makes for real security problems such as loss of company secrets and other financial data.