Maybe you are thinking of the place where you turn on WiFi Updates ??
Settings->MyMaps->Update Maps-> (Connect to a WiFi network / OK)
That gives a list of nearby wifi networks. You choose one and enter the password if you are wanting to enable Wifi updates.
But I don't know how you disable it if you have set it up - but try selecting a neigbours network and typing in the wrong password - and leave it like that.
Also In Settings ->Wireless Networks -> WiFi -- Check whether you have any 'Saved Networks' in place. If so, I guess that there is an option to remove it. I am not going to conenct to my network to try it out !! Also in the same WiFi menu untick Enable Wireless Networks.
I have observed that Wireless Networks have been turned on - but I do not know when. It certainly wasn't me. I have had two replacement XTs, so it might have been then, or it might have been when I have installed the latest software. I don't know. Keep an eye on it after software updates. Garmin do that sort of trick with Express - they reset it to stay resident in the computer, so after each Express update, I have to remember to turn that option off.