[originaltext] What is the difference between a computer virus and a compute

What is the difference between a computer virus and a computer worm? Both can infect and damage computer systems. However, computer viruses and computer worms differ in the way they reproduce and spread. A virus, which is short for "vital information resources under siege", is a program or code that secretly enters a computer by piggybacking on e-mail messages, files, or programs shared between two different computer systems. Then the virus infects its new host by attaching itself to the files within that computer and deleting or changing them or even overwriting entire programs. Just like a biological virus in the human body, a computer virus replicates itself so that it will continue to be contagious when data is shared with another computer system. In 2000, for example, the famous "Love Bug" virus, which traveled via e-mail messages, destroyed files in computers all over the world. Worms, too, are malicious programs that reproduce and spread. But unlike viruses, they do not need to attach themselves to other files. They are programs that run independently and spread on their own through computer networks. Thus they do not require human intervention to make their way from one computer to another. The famous Internet worm of 1988, for example, copied itself across the Internet, destroying many computer systems as it went. Currently, computer analysts are worried about the Sasser worm, which disabled computers in Britain, South Africa, and Taiwan.
Questions 29 to 31 are based on the passage you have just heard.
29. In what aspect do computer viruses and computer worms differ?
30. What can we learn about the "Love Bug" virus from the passage?
31. Which of the following statements is true about computer worms?