As location-aware advertising goes mainstream—like that Jack in the Box ad that appears whenever you get near one, in whichever app you have open at the time—and as popular apps harvest your lucrative location data, the potential for leaking or exploiting this data has never been higher.

It’s true that your smartphone’s location-tracking capabilities can be helpful, whether it’s alerting you to traffic or inclement weather. That utility is why so many of us are giving away a great deal more location data than we probably realize....