Do you always turn WiFi off on your smartphone before leaving the house or work? Read More ..
You might think there's no harm in having your WiFi turned on but not connected to a network, but that's not necessarily the case.
A wireless device goes through a discovery process in which it attempts to connect to an available wireless network. This may either be ‘passive’ - listening for networks which are broadcasting themselves - or ‘active’ - sending out probe request packets in search of a network to connect to.
Most devices use both passive and active discovery in an attempt to connect to known/preferred networks. So it's very likely that your smartphone is broadcasting the names (SSIDs) of your favourite networks for anyone to see.
This alone might be enough for someone to glean information about you: where you work, where you live or your favourite coffee shop for instance.
Even worse, an attacker could set up a rogue WiFi with the same SSID as the one you are trying to connect to with the aim of forcing your phone to connect and transfer data through it.