Wireless equipped laptops may be extremely vulnerable to wireless networks because, by default they may be configured to automatically connect to common network SSID’s, and assume it is your home network.  This may make your computer *very* vulnerable to snooping and attack and may give away your email passwords and other passwords.

How can you protect yourself? First, turn off your laptop’s wireless when not attempting to connect to a known network. Also, make sure your laptop doesn’t turn on its wireless when it can’t find an Ethernet connection. Most important, disable ad hoc networking, by clicking the Advanced button of the Wireless Network Connection Settings control panel to change it from Any available network (access point preferred) to Access point (infrastructure) networks only.

Source:   The Wireless Snare  By Robert Lemos