The Privacy Project has been underway for four months, and in that time we’ve learned quite a bit about what we do — and don’t — know about privacy.

Privacy is a complex, nebulous and constantly evolving issue, but amid the chaos and complexity, we have discerned four main themes: the ubiquity of surveillance and the ready availability of surveillance tools; our considerable ignorance of where personal data goes and how companies and governments use that data; the tangible harm of privacy violations; and the possibility that sacrificing privacy for other values (say, convenience or security) can be a worthwhile trade-off.

Surveillance Tools Are Readily Available

It’s unnervingly easy to violate the privacy of others — purposefully or inadvertently — using surveillance tools accessible to most everyone.

To show just how easy it is, Stuart A. Thompson, the graphics director for The New York Times Opinion Section, bought a set of targeted advertisements and then designed them to explicitly reveal the (usually hidden) information on which they operate. Targeted ads are often praised as a way for companies to help you find and buy products specific to your needs and interests — which seems harmless enough. But targeted ads can do more than that: They can influence your beliefs and manipulate your behavior.