Good WiFi security beats this
If the wifi you are using is encrypted with wpa2 and has wireless isolation enabled (and working , lots say they can do it but they can't) then this is not possible without breaking into the router. Sadly a surprising amount of places decide not to have a WiFi key for ease of connection. This is the case with the free WiFi on trains and is seems to be related to a bad implementation of its useless registration system
Biting the hand that feeds IT
