英语阅读理解第三篇

The computer virus is an outcome of the computer overgrowth in the 1980s. The term computer virus comes from the likeness between the viruses that harm the body and the harmful viruses. However, computer viruses are small programs. They reproduce by attaching a copy of themselves to another program.

Once attached to another program, viruses then look for other programs to “infect”. In this way , the virus can spread quickly throughout a single computer or an entire network when it infects a LAN or a multi-user system. At some point, the virus attacks according to how it is programmed. The timing of the attack can be linked to a number of situations, such an a certain time or date, the presence of a particular object, the security level of the user, and the number of times a program is used .Similarly, the pattern of attack comes in different ways .The so-called“harmless” viruses might simply show a message, like the one that infected IBM’s main computer system in 1987 with Christmas greetings. Harmful viruses are designed to damage the system. They can wipe out data, cross out information , or rewrite the hard disk.

Main Types of Viruses

There are four main types of viruses: shell, intrusive(侵扰的),operating system, and source code(源代码).

Shell viruses wrap themselves around a host program, but don’t change it .Shell programs are easy to write, which is why about half of viruses are of this type.

Intrusive viruses invade an existing program and actually place a part of them into the host program. Intrusive viruses are hard to write and very difficult to remove without damaging the host file.

Shell and intrusive viruses usually attack executable program files—those with a .com or .exe extension, although data files are also at risk.

Operating system viruses work by replacing part of the operating system with their wen code. They are very difficult to write and have the ability, once loaded, to take total control of your system.

Source ode viruses are intrusive programs that are inserted into a source program such as those written in Pascal prior to the program being followed. They are the least common viruses because they are not only hard to write, but also have a limited number of hosts compared with the other types.

Be Cautious About the Second Network Viruses

Do you believe it? Network viruses can steal money! And they are coming for your computer right now. So far the Internet has become the main channel through which computer viruses spread. Even without getting information from the network, your computer can be infected by the second network computer viruses, which are hidden in some machines on the network.

The virus that can steal your money is a kind of the second network viruses. It was designed and inserted in some machines on the network. When your computer is linked to one of these machines, the virus will invade your hard disk and search whether Intuit Quicken, an accounting program, is installed. One of this accounting program’s functions is to transfer accounts automatically. Once the program is infected, your money will be transferred to an additional account opened by the virus program without anybody knowing it.

puter viruses are small programs, which________.

A)are similar to the viruses that harm the human body

B)invade a living cell and produce other viruses