Nobody is literally forced to join an online social network, and most networks we know about encourage,
but do not force users to reveal - for instance - their dates of birth, their cell phone numbers, or where
they currently live. And yet, one cannot help but marvel at the nature, amount, and detail of the personal
information some users provide, and ponder how informed this information sharing is. Changing cultural
trends, familiarity and confidence in digital technologies, lack of exposure or memory of egregious misuses of
personal data by others may all play a role in this unprecedented phenomenon of information revelation. Yet,
online social networks’ security and access controls are weak by design - to leverage their value as network
goods and enhance their growth by making registration, access, and sharing of information uncomplicated.
At the same time, the costs of mining and storing data continue to decline. Combined, the two features imply
that information provided even on ostensibly private social networks is, effectively, public data, that could
exist for as long as anybody has an incentive to maintain it. Many entities - from marketers to employers to
national and foreign security agencies - may have those incentives.