Multiple Networks being read but there is only one network set up.

Alright we have our work network set up with about 10 computers and 10 VOIP phones on it. We have our modem that goes into a Netgear Router and then connects through a dummy switch which connects all of our computers and phones in the office. What is going on is that on a semi regular basis several computers in the office are readying 2 networks but there is only 1 network set up. None of...