The computer network is a creation of the electronic age. In a computer system, a hacker is worse than a thief entering your house. He could go through anyone's electronic mail or add to, change, distort or delete anything in the information stored in the computer's memory. He could even take control of the entire system by inputting his own instructions in the software. He could shut the computer down whenever he wished, and no one could stop him. Then he could program the computer to erase any sign of his ever having been there. Hacking, our electronic-age term for computer break-in, is more and more in the news: A dissatisfied former insurance-company employee wipes out information from payroll files. A student sends out a 'virus', a secret and destructive command, over a national network. The virus copies itself at lighting speed, jamming the entire network—thousands of commercial and government computer systems. Now exists the possibility of terrorism by computer. Destroying a system responsible for air-traffic control at a busy airport or the telephones of a major city is a relatively easy way to spread alarm. Yet neither business nor government has done enough to strengthen its defenses against attack. For one thing, such defenses are expensive; for another, they may interrupt communication—the main reason for using computers in the first place. Why does the writer mention 'a thief' in the first paragraph?