It's easy to load a small library of electronic books into your laptop or handheld organizer and take it on the bus or to the beach. But try to make backup copies of those e-books or loan one to a friend, and you'll run smack into the digital equivalent of an electrified fence. The problem is that once a literary work has been liberated from the printed page, it's potentially vulnerable to unlimited digital piracy-a danger that makes most e-book publishers insist on strict software controls to prevent anyone but the purchaser from opening an e-book file.

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