Viruses are human－made software programs【C1】______specifically to wreak havoc on personal

Viruses are human-made software programs【C1】______specifically to wreak havoc on personal computers and networks. The【C2】______of contracting one of these computer viruses over the Internet has increased dramatically. Typically, you get a virus by opening e-mail【C3】______.

Some viruses are relatively【C4】______to individuals. They just【C5】______themselves to【C6】______messages or e-mail themselves to all the people listed in your address book. The sudden flood of email【C7】______mail servers, causing the system to【C8】______.

Other viruses are more【C9】______,and may lie asleep until a certain date. Then they【C10】______to life to do their dirty【C11】______. Sometimes a strange message appears on your screen, or data and programs may be【C12】______. In the worst case, all the contents of your hard drive may be【C13】______out. These【C14】______programs start on one computer, then replicate quickly,【C15】______other computers around the world.

In 1988, a student at Cornell University sent out a virus by【C16】______, nearly【C17】______the Internet to its knees. More recently, the "I Love You" virus caused over $1 billion in lost【C18】______as it【C19】______e-mail systems worldwide. Last year【C20】______, 10, 000 new viruses, worms and Trojan horses were unleashed.

【C1】

A．existed

B．discovered

C．created

D．manufactured