A federal judge in Illinois has ruled that intercepting traffic on unencrypted WiFi networks is not wiretapping. The decision runs counter to a 2011 decision that suggested Google may have violated the law when its Street View cars intercepted fragments of traffic from open WiFi networks around the country.

The ruling is a preliminary step in a larger patent trolling case. A company called Innovatio IP Ventures has accused various "hotels, coffee shops, restaurants, supermarkets," and other businesses that offer WiFi service to the public of infringing 17 of its patents. Innovatio wanted to use packet sniffing gear to gather WiFi traffic for use as evidence in the case. It planned to immediately delete the contents of the packets, only keeping the headers. Still, the firm was concerned that doing so might violate federal privacy laws, so it sought a preliminary ruling on the question.

Federal law makes it illegal to intercept electronic communications, but it includes an important exception. It's not illegal to intercept communications "made through an electronic communication system that is configured so that such electronic communication is readily accessible to the general public."

Judge James Holderman ruled that this exception applies to Innovatio's proposed packet sniffing. In the Google Street View case, a California judge had suggested that WiFi communications were not public, even if they were sent without encryption. But Judge Holderman reached the opposite conclusion:

Innovatio is intercepting WiFi communications with a Riverbed AirPcap Nx packet capture adapter, which is available to the public for purchase for $698.00. A more basic packet capture adapter is available for only $198.00. The software necessary to analyze the data that the packet capture adapters collect is available for download for free. With a packet capture adapter and the software, along with a basic laptop computer, any member of the general public within range of an unencrypted WiFi network can begin intercepting communications sent on that network. Many WiFi networks provided by commercial establishments (such as coffee shops and restaurants) are unencrypted, and open to such interference from anyone with the right equipment. In light of the ease of "sniffing" WiFi networks, the court concludes that the communications sent on an unencrypted WiFi network are readily available to the general public.

Legal scholar Orin Kerr disagrees with Judge Holderman's reasoning. "No one suggests that unsecured wireless networks are set up with the goal that everyone on the network would be free to read the private communications of others," he wrote. "In my view, that ends the matter: the exception doesn’t apply, and the interception of the contents of wireless communications is covered by the Wiretap Act."

Google's Street View case is now before the United States Court of Appeals for the Ninth Circuit—and the company no doubt hopes that the appellate court sees things Judge Holderman's way.