It very well could be that during the removal of the virusses a file needed for a proper connection has been removed or changed. What you can try is this: Remove the modem from device manager, reboot and reinstall it. This should restore your connection settings. If needed recreate the dial up connection.

I am sure that if one of the Alwill members have an idea they will do so very soon. Just wait a little before trying this to see if others have any suggestions which you can try 1st.