In the comment thread to my post on the symposium about applying the Fourth Amendment to computers, commenter "New World Dan" states:

This is one area that drives me nuts. I can't think of one single case where conventional law was inadequate to address 4th amendment issues in the "Digital Age". Internet records are really no different than phone, library or financial records. That, of course, hasn't stopped politicians, lawyers and judges from making it more complicated than it is, though.

  Dan's comment is a bit misleading: Pretty much everyone agrees that non-content Internet records should be treated exactly like non-content phone, library, or financial records. But I take his broader point to be that there's nothing new here. We can apply the Fourth Amendment to computers by applying simple analogies to "conventional law."

  I certainly appreciate Dan's instincts. Analogies are extremely important in this area, as they are in most areas of technology law. But the fact that they are important doesn't mean that they are simple or sufficient.

  For example, if you think an e-mail message is just like a postal package, is e-mail more like a first-class package (protected by the Fourth Amendment) or a fourth-class package (not protected)? If you think e-mails are exactly like telephone calls, are they more like landline calls (protected by the Fourth Amendment) or cordless phone calls (not protected)? And what do you do with information like URLs — what's the "phone, library, or financial records" analogy to them? Are URLS more like the contents of phone calls or just records of the call?

  "New World Dan" may find these questions easy, but I suspect most of us don't. And those who find these issues easy probably disagree with each other as to what the easy answers should be. The problem, I think, is that communications networks work by sending information out into the network, and we have an intuitive sense (for good practical reasons beyond the scope of this post) that some information should be protected and other information shouldn't be. This means that we'll always have competing "conventional law" analogies that appear plausible: one side will pick an analogy to protected information, the other to unprotected information.

  As I see it, choosing among these competing analogies generally requires a broader normative theory of what should make a difference. Otherwise it's "turtles all the way down." Or at least it's turtles down to the foundational premise that the Fourth Amendment protects the inside of the home but not public spaces, which I think can plausibly be used to support nearly any result when applied to communications networks.

  Consider Olmstead v. United States, the 1928 case that considered whether wiretapping was a Fourth Amendment search when agents tapped a private telephone line from the public street. Each side offered an analogy from "conventional law" to solve how the Fourth Amendment applied to the new technology of the telephone. To the majority, the analogy was public speech: wiretapping from a public street was just like listening to someone shouting their communications into the public square. To the dissent, the analogy was invading a private space: wiretapping was just like breaking into someone's home and listening to their private conversations.

  Which side was right? To answer this, I think you need to go beyond simply applying "conventional law." The trick is how to apply conventional law, and there are substantial arguments for and against a very wide range of alternatives. Picking among the options requires a broader theory, which is why these questions are both interesting and hard.

  For more on these issues, check out my essay, "Digital Evidence and the New Criminal Procedure," which was published in the Columbia Law Review in 2005.