• by Wendy Davis , Staff Writer @wendyndavis, January 24, 2012

In a landmark decision addressing privacy in the digital era, the Supreme Court said this week that the police violated a suspect's rights by installing a GPS device on his car without a warrant.

While the case dealt with whether the government can track people suspected of crimes, the judges' reasoning could influence judges in a broad swath of privacy disputes that don't involve surveillance by police officers.

In particular, Justice Sonia Sotomayor said in a concurring opinion that people might have an expectation of privacy in certain data -- like Web sites visited, books purchased and email addresses in their contact lists -- even when they share such information with outside companies.

That's notable because, in the past, some judges have held that Web users have no privacy interest in information once it's shared with a company. Most recently, a federal magistrate judge in Washington, D.C. ruled several weeks ago that Web users couldn't even contest subpoenas for data linking their IP address to their names without first placing their names on the record. “Individuals who subscribe to the internet through ISPs simply have no expectation of privacy in their subscriber information,” the judge wrote in that case.

But Sotomayor's statements call into question whether such reasoning is valid. “It may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties,” she wrote. “This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks. People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers.”