It is, to use a clumsy metaphor, like a king who builds a library, and then builds a moat around it. Moats, towers, and guards can keep it safe, allowing only the king to carry books in or out. The internet, instead, gives us thousands upon thousands of libraries, with people freely adding and copying books and traveling between libraries. At any moment, someone could submit a book that spontaneously combusts, or a book that, when opened, locks the librarians out until they pay a ransom. It is perhaps no wonder that this week the Director of National Intelligence James Clapper named the internet of things the greatest threat facing America today.