What Is Wi-Fi Sniffing?

When you are away from home and need to connect to the Internet via your computer or mobile device, wireless networks available to the public or authorized users can provide you with online access. However, some open wireless networks may not show up in your device’s list of nearby Wi-Fi hotspots. Wi-Fi sniffing tools can help you locate open networks that may not be visible.

When individuals and organizations set up a wireless local-area network, or WLAN, with a wireless router, they can choose to broadcast the name of the network, also known as the service set identifier, or SSID, so anyone in the vicinity can detect the presence of the Wi-Fi hotspot. WLAN owners can also set up password authentication for accessing the network or leave it open so anyone with a wireless device can connect. However, some WLAN owners choose not to broadcast the name of the network. This is a frequent practice of college and professional athletic teams that want to limit access to Wi-Fi in arenas to employees and members of the media during games. If you cannot find the SSID of a network you have permission to access using the built-in software of your device or computer, you can use sniffing tools to scan nearby hotspots to find it.

Software for scanning Wi-Fi networks within reach of your device’s wireless antenna not only monitor your own Wi-Fi network, but also show visible nearby networks, including SSIDs hidden by WLAN owners. Examples include InSSIDer, a paid program available for Windows and Mac computers, as well as Android devices; KisMac, a free Wi-Fi monitoring tool for Mac OS X; and Kismet, a free Wi-Fi monitoring tool that runs on Linux computers (see Resources). Apple prohibits software for Wi-Fi sniffing on its devices, and removed sniffing apps from its App Store in 2010.

The practice of “wardriving,” also called access point mapping, involves roaming around in a car detecting Wi-Fi networks using sniffing apps. Participants in this activity use Wi-Fi monitoring software to detect the networks, and then upload the GPS coordinates of the hotspots to websites like Geomena and openBmap, making it easier for others to find these hotspots.

When you use a Wi-Fi sniffer, you may detect open networks of homeowners and businesses who have not secured their WLAN or have weak security. Even though these networks are open or weak, it is unethical to connect to someone else’s network without their permission -- you would not want strangers accessing your own Wi-Fi network and potentially engaging in illegal activity via online access that you pay for. As of early 2014, federal courts are still figuring out the legality of unauthorized Wi-Fi sniffing, though in 2013 a federal court ruled that collecting unencrypted content from wireless routers is not exempt from the Wiretap Act.