What is a computer virus
1. The characteristics of computer virus is that a virus is a program, so it has all the characteristics of a program. In addition, it is also concealed, latent, infectious and destructive.
The virus's usual way of expansion is to copy its own destructive code into other useful code. Its spread is based on the operation of the computer system and the reading and writing of disks. 
Figure 2-14 Virus working process
2. Virus classification Viruses are divided into benign viruses and malignant viruses according to their degree of harm; they can be divided into guided type, file type, compound type and network type according to the objects they invade.
3. In the early days of computer applications, floppy disks were the main method of spreading viruses. With the rapid development of the network, floppy disks tended to be eliminated. The network carrier has added wings to the spread of viruses. According to statistics, the virus transmitted through the attachment of the network mail system exceeds 60% of the total virus transmission path. Following the "CIH" virus, new types of network viruses such as "Romeo and Juliet", "Smart Virus", and "Shockwave" have appeared.
Computer virus prevention
Pay attention to the following links to prevent computer viruses:
l Create an emergency boot disk and the latest emergency repair disk.
l When using external disks or files from other machines, you must first use antivirus.
l Write-protect disks that do not require write operations.
l Install virus detection software for the computer, check the virus regularly, and pay attention to update in time.
l Install a virus firewall or protective card specifically for anti-virus and anti-virus for the computer.
When you are online, try to minimize the exchange of executable code, and try to work offline when you can work offline.
Virus detection and elimination
1. Virus detection The virus is latent in the computer, and it is difficult to be discovered without being excited. Therefore, carefully observe the abnormal phenomenon of the system. Generally, if the computer is abnormal, first determine whether it is caused by computer hardware. If the hardware system is normal, you should consider whether it is infected with a computer virus. If the virus detection software or hardware installed in the computer detects a virus, it should take corresponding measures immediately. The computer may also be infected with a virus when the following occurs:
l The computer startup speed becomes very slow for no reason.
l A large amount of memory is occupied for no reason.
l often crash for no reason.
l The disk file becomes longer for no reason.
l The disk read and write time becomes longer.
l An inexplicable display message appears.
Unreasonable results in the program operation.
2. Virus removal The virus removal is generally performed using anti-virus software. The principle of antivirus software is exactly the opposite of that of viruses. It can remove thousands of viruses at the same time and has no effect on the data in the computer.
Common antivirus software include KV3000, Norton, Rising, Kingsoft, etc.
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