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If you've used Wi-Fi in an airport or conference center recently, you've probably seen at least one network called "Free Public Wi-Fi." Upon closer inspection, you may have noticed that this SSID isn't being advertised by an infrastructure access point, but rather a nearby ad hoc node. This enticing SSID – and others like it – are being spread between hotspot users in a manner that resembles virus infection.
Suppose you're sitting at an airport gate, waiting for your flight. You fire up your Windows laptop, see "Free Public Wi-Fi," and attempt to connect to it. After you connect, perhaps you get an automatic private IP address or no IP address at all. You almost certainly don't reach the Internet because you are, in fact, connected directly to some other hapless Wi-Fi user sitting right there at the airport gate.
Before your flight departs, you close your laptop and board your plane. After you deplane at the next city and open your laptop, your Wi-Fi card tries to automatically reconnect to "Free Public Wi-Fi." Others sitting around you see this SSID being advertised by your laptop, and try to connect to you. This cycle repeats itself, spreading "Free Public WiFi" SSID from traveler to traveler, city to city.
AirTight Networks studied this phenomenon by conducting a formal survey of 26 airports throughout the US and Asia. According to published results, these "viral SSIDs" were spotted at 21 airports, infecting approximately 10 percent of the clients observed during surveys.
Just connecting to "Free Public WiFi" is not necessarily harmful. However, your laptop's willingness to connect automatically to strangers exposes you to all sorts of peer-to-peer attacks. To avoid this, configure your Wi-Fi adapter to disallow ad hoc connections and automatic connections to "non-preferred networks." Remove unwanted names from your list of available networks and, in the future, whenever you connect to a new hotspot, reconfigure that available network entry to connect only at your request. These simple steps can help you avoid falling victim to "Free Public WiFi" and other viral SSIDs.
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