There are free downloads from the internet that allow someone to "sniff" (see) your every keystroke while browsing the internet. Think about this the next time you are doing online banking, paying bills online or accessing your credit card statements. Your user name, password and account information could be visible outside your home or office if your Wi-Fi is not set up securely. ...
There are people that drive around neighborhoods and cities with a laptop or phone and an antenna that have the sole purpose of detecting your Wi-Fi device. They upload this information to maps that are readily available on the internet showing your SSID and exact location. They also are checking to see if the hot spots are secure.
1: Change Default Administrator Passwords (and Usernames)
2: Turn on Wireless Network Encryption
3: Change the Default SSID
4: Enable MAC Address Filtering
5: Disable SSID Broadcast
6: Stop Auto-Connecting to Open Wi-Fi Networks
7: Position the Router or Access Point Safely
8: Assign Static IP Addresses to Devices
9: Use Firewalls and Security Software
10: Turn Off the Network During Extended Periods of Non-Use