A federal judge has found that Google can be held liable for damages for secretly intercepting data on open WiFi routers, dealing the search giant a serious legal setback for activity it has engaged in across the United States for years.

That ruling was handed down late Wednesday by a Silicon Valley federal judge presiding over nearly a dozen combined lawsuits seeking damages from Google for eavesdropping on open Wi-Fi networks from its “Street View” mapping cars. The vehicles had been equipped with WiFi–sniffing hardware to record the names and MAC addresses of routers to improve Google location-specific services.

“The court finds that plaintiffs plead facts sufficient to state a claim for violation of the Wiretap Act. In particular, plaintiffs plead that defendant intentionally created, approved of, and installed specially-designed software and technology into its Google Street View vehicles and used this technology to intercept plaintiffs’ data packets, arguably electronic communications, from plaintiffs’ personal Wi-Fi networks,” U.S. District Judge James Ware ruled. “Further, plaintiffs plead that the data packets were transmitted over Wi-Fi networks that were configured such that the packets were not readable by the general public without the use of sophisticated packet sniffer technology.”

Judge Ware’s ruling is important not only to Google, but to the millions who use open, unencrypted WiFi networks at coffee shops, restaurants or any other business trying to attract customers.

Google, in seeking a dismissal, claimed it is was not illegal to intercept data from unencrypted, or non-password-protected WiFi networks. Google said open WiFi networks are akin to “radio communications” like AM/FM radio, citizens’ band and police and fire bands, and are “readily accessible” to the general public — a position rejected by Ware.

Google said it didn’t realize it was sniffing packets of data on unsecured WiFi networks in about a dozen countries over a three-year period until German privacy authorities began questioning what data Google’s Street View cars were collecting. Google, along with other companies, use databases of Wi-Fi networks and their locations to augment or replace GPS when attempting to figure out the location of a computer or mobile device.

No hearing date has been set.

Google did not immediately respond for comment.

(Will be updated)

Photo: dspain/Flickr