It's unlikly but possible for a virus to just jump around a network. Viruses come in many flavors but most are from opening a mail attachment or physically copying the infected file from one computer to another. Now your first issue, Im going to take a shot from the hip because you did not give that much info but go to your network properties, you should see an Authentification tab. Make sure that the IEEE 802.1x check box is UNCHECKED. let us know