Facebook knows your likes and dislikes, not to mention who your friends are. Amazon knows your taste in books and anything else you shop for at its online superstore. Google knows what you research or wonder about. And other websites - including this one, if you're reading at Philly.com - can track your browsing and clicking habits as you navigate from site to site in the same ad networks.
But what does your wireless carrier or Internet provider know about you? Potentially, all those same things and much, much more - which is why changes in Verizon and Verizon Wireless' data policies are stirring concern among privacy advocates and members of Congress.
The new data policies allow customers to opt out of what Verizon describes, in part, as "new ways to advertise to mobile users and wireline broadband customers" - a choice a Verizon official stressed when I called to ask about the company's changes in terms.
But it's the flip side of that - Verizon's inclusion-by-default approach - that most disturbs advocates such as John Simpson, of California's Consumer Watchdog.
"They've changed the rules in midstream to allow them to do whatever they want with the data," Simpson says. "At the very least, if they do this, they should do it as an opt in."
It's hard to tell exactly what Verizon and Verizon Wireless plan to do, although news reports and critiques center on the expectation that Verizon and its mobile affiliate want a bigger piece of the growing, lucrative pie known as behavioral marketing - delivering ads to consumers based on profiles of their behavior.
According to the website Digital Trends, "the data collected will include all Web sites visited through a Verizon phone including keywords used in a search engine, the location of the device and all downloads of apps as well as which apps are getting the most use."
Verizon officials declined to answer questions, beyond e-mailing a statement dated Monday that said the companies' new advertising program "does not use web surfing information or device location information."
One point of confusion appears to be that Verizon and Verizon Wireless have announced two new programs, one delivering ads and another involving "creation of new types of aggregate business and marketing programs."
Verizon's statement added, "Any information shared in these programs will be non-personally identifiable, meaning that none of the information will connect back to a specific customer."
Simpson, the privacy advocate, was probably exaggerating in saying that the new Verizon policies allow the companies "to do whatever they want with the data."
But Verizon's new policy does appear to mark an about-face from a pledge made three years ago at a Senate hearing, when it joined AT&T in promising not to track customers' Web behavior without explicit permission.
"Verizon believes that before a company captures certain Internet-usage data . . . it should obtain meaningful, affirmative consent from consumers," Verizon vice president Thomas J. Tauke said, according to a September 2008 Washington Post report.
Companies, like people, are allowed to shift course. When I asked Chris Hoofnagle, director of information-privacy programs at the University of California at Berkeley's law school, about Verizon's shift, he voiced surprise that it hadn't occurred sooner.
But like other privacy advocates, Hoofnagle also said there were special reasons for concern when network owners venture into a field, behavioral marketing, that has already stirred considerable controversy.
"The standard should be opt in," Hoofnagle said. "If consumers really want more targeted advertising mediated from their own service provider, which they are directly paying, the service provider should get consent first."
Contact columnist Jeff Gelles
at 215-854-2776 or email@example.com.
Want to opt out of Verizon's new privacy terms? Verizon Wireless customers can call 1-866-211-0874 or visit www.vzw.com/myprivacy. Verizon landline customers can change privacy settings at www.verizon.com/myaccount.