Elinor Mills/CNET

LAS VEGAS -- Got a Wi-Fi network? If someone, say Google or the government, sniffs your open network, you may think you're legally protected. Don't be so sure.

It remains unclear whether the law protects your unencrypted Wi-Fi from interception, because there are differing interpretations and lack of court precedent, Kevin Bankston, senior counsel at the Center for Democracy and Technology, said in a session at Defcon yesterday.

The federal wiretap statute prohibits sniffing of contents of communications by a device unless the contents are readily accessible to the general public. If the network is password-protected you're fine. But under the definition of "readily accessible to the general public," unencrypted radio communications may not be covered, Bankston said.

Years ago, Congress amended the wiretap law to include protection for unencrypted cordless phone calls because millions of people were relying on them with the expectation of privacy. The courts have not yet issued a similar ruling for Wi-Fi traffic.

The question is before the courts in a case involving Google and its Street View cars, which were found to be capturing e-mail, text messages, passwords, and other data as they drove around taking pictures for Street View. During the class-action lawsuit brought against Google, the company argued that because the data was not encrypted, it was not covered by the wiretap law. The plaintiffs argued, and the court agreed, that Wi-Fi is not the type of "radio communication" Congress intended, so Wi-Fi communications may be protected under the wiretap law even if they're not encrypted, Bankston said. Google has appealed the ruling to the Ninth Circuit Court of Appeals.

Meanwhile, the Federal Communications Commission fined Google $25,000 earlier this year for obstructing its investigation into the Wi-Fi sniffing matter, but the agency was unable to conclude that the company had violated the law, Bankston said.

To confuse matters, the law may provide protection for some, but not all, of the wireless spectrum that's used by Wi-Fi router channels. Under one reading of the statute, only channel 11 is fully protected, while certain frequencies in channels 7 through 10 are protected, and channels 1 through 6 are not protected at all, according to Bankston.

Bankston says the statute should cover open Wi-Fi networks, but he made it clear that he was not taking an official policy position on the matter. He said he and Matt Blaze, a computer science professor at the University of Pennsylvania, debated the topic to highlight the lack of clarity in the law and to start a discussion about how the law should treat the interception of open Wi-Fi. Both men said they could easily have swapped sides. "The law is a mess," Bankston said.

Blaze, who does research involving radio communications interception, argued that creating a strict law could stifle innovation. For instance, it could affect how people use so-called "software-defined" radio, which uses software to select particular signals when they're broadly intercepted, he said.

"There are legitimate reasons to intercept radio waves over the air," he said. "Doing what Google did has led to incredibly useful things," such as building out a location database that is an alternative to GPS.

Eventually, it won't be an issue, because new routers are shipped with encryption enabled by default. But about one-quarter of the hot spots are still open, Bankston said.

The problem is not just that content can be sniffed, but what snoops can do with it. "There is the possibility for mass surveillance" and tying traffic to a specific address, Bankston said.

So, until this all gets sorted out it's best to use a password to protect your Wi-Fi network, and if you insist on leaving it open, set the router to channel 11.