In order to understand how companies share data, Geambasu devises clever ways to track the repercussions. Her latest software uses a series of “shadow accounts” to see how ads change when certain phrases are used. She found, for instance, that when people email about topics like cancer or depression, ads for spiritual meditation services will appear. What's more, if people then click on those ads, they've confirmed the targeting was effective. Other programs she’s designed make data self-destruct after a set period of time, help users track what information they’ve entered where, and limit data breaches from lost or stolen phones.