The Facebook just released a new feature that shows all the recent changes from your friends on your main page. Less than a day later, there are multiple groups protesting this as an invasion of privacy; the largest I've found is nearly 25,000 students strong. This is a very important reaction that we should pay attention to: a great many people feel their privacy has been invaded, but no new information has been revealed! The new feature only aggregates publicly available information. How could that be an invasion of privacy?

Because our previous conception of privacy, as public/private, is a flawed dichotomy that must be discarded in the face of changing technology. Data is not merely private or public, known or not known. Data has an associated cost of retrieval which is either high or low. The strength of this reaction to the new feature might have caught its creators by surprise, but it shouldn't have. After all, The Facebook's walled-garden approach to schools is largely responsible for its popularity, and that approach is entirely based around increasing the cost of accessing data. No one really believes that information they enter there is private, just that it will be relatively difficult for outsiders to find. A huge amount of information had been entrusted to The Facebook with the understanding that it would be available only to other users of The Facebook, and to them only so long as they paid the time cost of looking for it. Now that time cost has been reduced to nearly zero, privacy has been reduced correspondingly. The protesting students' instinctive reaction is precisely correct; the privacy bargain has been unilaterally modified.

This is same kind of invasion of privacy being proposed by the Bush Administration in the Total Information Awareness project. No private information would go into the database, and yet aggregating that data into one place is still an invasion of privacy. We all agree that our whereabouts are not secret when we enter public spaces, yet I doubt many of us would be comfortable with the government recording our every movement. That our purchasing histories are public is no big deal when accessing one takes effort and time; they are still mostly private because most people will not spend the time to find them.

Data aggregation is an invasion of privacy because it reduces the cost of access to that data, and cost of access is the continuum upon which "public" and "private" are poles.

  • Update: 4 hours later, it's up to 85,000 students.
  • Update: A day later, it's up to 280,000 students.
  • Update: A few days later, it maxed out around 750,000 students.