Military cybersomethings

You can hardly read the news without seeing dire warnings of national security problems lurking in our computers. If it isn´t some country stealing some other country´s commercial secrets—just who´s the victim and who´s the thief varies with the teller, of course—it´s the threat of a "cyber Pearl Harbor" or "cyberterrorism" or "cyberwarfare" or "cyberespionage" or "cyber disturbing the peace" or cybersomething-or-other. What are all of these things? Are they real? And what should "we"—one nation, or the whole world—do about them?