People tend to think of computers as isolated machines, working away all by themselves. Some personal computers do without an outside link, like someone's secret cabin in the woods. But just as most of homes are tied to a community by streets, bus routes and electric lines, computers that exchange intelligence are part of a community local, national and even global network joined by telephone connections.
　　The computer network is a creation of the electric age, but it is based on old-fashioned trust. It cannot work without trust. A rogue (流氓) loose in a computer system called hacker is worse than a thief entering your house. He could go through anyone's electronic mail or add to, change or delete anything in the information stored in the computer's memory. He could even take control of the entire system by inserting his own instructions in the software that runs it. 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, intelligent kids vandalizing（破坏）university records, even pranking (恶作剧) about in supposedly safeguarded systems. To those who understand how computer networks are increasingly regulating life in the late 20th century, these are not laughing matters. A potential for disaster is building: A dissatisfied former insurance-company employee wipes out information from some files; A student sends out a "virus", a secret and destructive command, over a national network. The virus copies itself at lightning speed, jamming the entire network thousands of academic, commercial and government computer systems. Such disastrous cases have already occurred. Now exists the possibility of terrorism by computer. Destroging a system responsible for air-traffic control at a busy airport, or knocking out the telephones of a major city, is a relatively easy way to spread panic. 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.
1. People usually regard computers as _________.
A. part of a network           
B. means of exchanging intelligence
C. personal machines disconnected from outside
D. a small cabin at the end of a street .
2. The writer mentions “ a thief ”in the second paragraph most probably to _________.
A. show that a hacker is more dangerous than a thief
B. tell people that thieves like to steal computers nowadays
C. demand that a computer network should be set up against thieves
D. look into the case where hackers and thieves are the same people
3. According to the passage , a hacker may do all the damages below EXCEPT _________.
A. attacking people’s e-mails .      B. destroying computer systems .
C. creating many electronic-age terms .      
D. entering into computer systems without being discovered
4. By saying “ Now exists the possibility of terrorism by computer ”(the underlined ) the writer means that________.
A. some employees may erase information from some files
B. students who send out a “ virus ”may do disastrous damages to thousands of computers
C. some people may spread fear in public by destroying computer systems
D. some terrorists are trying to contact each other using electronic mails