Analysis:
Broadly speaking, all programs that can cause computer failures and destroy computer data are collectively called computer viruses. According to this definition, such as logic bombs and worms can be called computer viruses. 1994 February 18, China officially promulgated and implemented the regulations on the security protection of computer information systems in People's Republic of China (PRC). Article 28 of the regulations clearly pointed out: "A computer virus refers to a group of computer instructions or program codes that are compiled or inserted in a computer program, destroy computer functions or data, affect the use of computers, and can replicate themselves." This definition is legal and authoritative.
In the early days of computer viruses, when it comes to the harm of computer viruses, we often pay attention to the direct damage of viruses to information systems, such as formatting hard disks and deleting file data, so as to distinguish malignant viruses from benign viruses. In fact, these are just part of the bad trajectory of the virus. With the development of computer application, people deeply realize that any virus may cause serious damage to computer information system.
The main hazards of computer viruses are:
1. The direct destruction of computer data information by virus excitation.
Most viruses directly destroy the important information and data of the computer when activated. The methods used include formatting disks, rewriting file allocation tables and directory areas, deleting important files or rewriting files with meaningless "junk" data, and destroying CMO5 settings. Disk killer virus (D 1SK KILLER) contains a counter, which is activated within 48 hours after the hard disk is infected. When activated, the screen displays "Warning! ! Please don't turn off the power or take out the disk when the black disk is running! "(Warning! D 1SK KILLER ll 1 is working, don't turn off the power or take out the disk), overwrite the hard disk data. D 1SK killer's damaged hard disk can be repaired with antivirus software, so don't give up easily.
2. Occupy disk space and damage information
Viruses parasitic on the disk always occupy a part of the disk space illegally. The general occupation method of boot virus is that the virus occupies the boot sector of the disk itself and transfers the original boot sector to other sectors, that is, the boot virus covers a disk sector. Overwritten sector data will be permanently lost and cannot be recovered. File virus is infected by some DOS functions, which can detect the unused space of the disk and write the infected part to the unused part of the disk. Therefore, in the process of infection, the original data on the disk is generally not destroyed, but the disk space is illegally occupied. Some file viruses spread very fast, infecting a large number of files in a short time, and each file is elongated to varying degrees, resulting in a serious waste of disk space.
3. Seize the system resources
Except for a few viruses such as VIENNA and CASPER, most other viruses reside in memory dynamically, which will inevitably seize some system resources. The basic memory length occupied by a virus is roughly equivalent to the length of the virus itself. The virus preempted the memory, resulting in memory reduction, and some software could not run. In addition to occupying memory, viruses will preempt interrupts and interfere with system operation. Many functions of computer operating system are realized by interrupt calling technology. Viruses are excited to be infected, and always modify some related interrupt addresses and add virus "bootleg" in the normal interrupt process, thus interfering with the normal operation of the system.
4. Affect the running speed of the computer
After the virus enters the memory, it not only interferes with the system operation, but also affects the speed of the computer, mainly in the following aspects:
(1) virus has been monitoring the working state of the computer in order to judge the infection excitation conditions, which is redundant and harmful to the normal running state of the computer.
(2) In order to protect themselves, some viruses encrypt not only the static viruses on the disk, but also the dynamic viruses that enter the memory. Every time the CPU addresses the virus, it needs to run a decryption program to decrypt the encrypted virus into legal CPU instructions before execution. At the end of the virus operation, re-encrypt the virus with a program. In this way, the CPU executes thousands or even tens of thousands of instructions.
(3) When infected with viruses, illegal extra operations should also be inserted, especially when infected with floppy disks, which will not only slow down the computer speed obviously, but also disturb the normal reading and writing order of floppy disks and make harsh noises.
5. Computer virus errors and unforeseen dangers
A big difference between computer viruses and other computer software is that viruses are irresponsible. Compiling a perfect computer software requires a lot of manpower and material resources. After a long period of debugging and improvement, the software can be online. But it is not necessary and impossible for virus makers to do so. Many computer viruses are hastily compiled and debugged by a person on the computer and then thrown away. After analyzing a large number of viruses, anti-virus experts found that most viruses have different degrees of errors. Another major source of error viruses is mutant viruses. Some beginners don't have the ability to compile software independently, out of curiosity or other reasons.
Modify other people's viruses, causing errors. The consequences of computer virus errors are often unpredictable. Anti-virus workers have pointed out in detail that Black Friday virus has 9 errors and Ping Pong virus has 5 errors. But people can't spend a lot of time analyzing thousands of virus errors. A large number of viruses with unknown errors spread, and the consequences are unpredictable.
6. The influence of computer virus compatibility on system operation.
Compatibility is an important index of computer software. Software with good compatibility can run in various computer environments, while software with poor compatibility is "picky" about operating conditions and requires model and operating system version. Virus compilers generally don't test viruses in various computer environments, so virus compatibility is poor, which often leads to crashes.
7. Computer virus has caused serious psychological pressure to users.
According to the statistics of relevant computer sales departments, after-sales users of computers suspect that "the computer has a virus" and make inquiries, accounting for more than 60% of the after-sales service workload. About 70% of them were found to have viruses, and 30% were only suspected by users, but in fact, the computer did not have viruses. So what is the reason why users suspect the virus? Most of them are computer crashes and abnormal software operation. These phenomena may indeed be caused by computer viruses. But not all. In fact, in the case of "abnormal" computer, it is difficult to ask an ordinary user to accurately judge whether it is caused by a virus. Most users trust viruses, which is undoubtedly necessary to protect computer security, but it often takes time and money. It's even harder to make up for the loss of formatting a disk just because you suspect a virus. Not only individual stand-alone users, but also in some large-scale network systems, it is inevitable to stop and identify viruses. In a word, computer virus hangs over the minds of computer users like a "ghost", causing great psychological pressure on people and greatly affecting the working efficiency of modern computers. The intangible losses it causes are incalculable.
Computer virus has a great influence on computer system. Most viruses destroy computer programs and data. The following describes the different damages and effects caused by the virus.
Some computer viruses, such as FormatC and Stoned Daniela, will unconditionally format the hard disk and delete all system files on the disk when triggered. Take AOL4Free Trojan horse as an example. It is attached to the email with AOL4FREE.COM as the file name. In fact, it is converted from batch files by using DOS utility)-BATEXEC 1.5 (this utility is used to convert some large batch files to improve speed).
This Trojan will first look for the file DELTREE.EXE in different directories under DOS, and then use this file to delete all files on the hard disk. When the file is deleted, it will display a DOS error message: "Bad command or file name" and an obscene message. If the virus can't find DELTREE.EXE, it can't delete files, but obscene information will still appear.
Some viruses, such as monkeys (stones. Empire. Monkey) and AntiEXE will infect the MBR and Dos boot sector of the master boot record, and then reduce the performance of the memory and hard disk until some messages or other damages appear when we use the computer.
Take AntiEXE as an example. When the master boot record (MBR) is loaded during the boot process, the virus will store the uninfected MBR in the location of O column, Side) O, Sector) 13 on the hard disk. Then the virus will put its virus code into MBR. And write the infected MBR to the position of cylinder) o, side) o and sector 1 in the hard disk. When the anti-Exe virus in memory is active, it will read the toxic MBR and/or DBS and reintroduce it into the clean copy. When MBR and/or DBS are installed during disk reading, the virus will find a specific *. EXE file (whose identity is currently unknown) and then destroy the file.
For another example, half will encrypt about half of the hard disk and display a message: the disk is half. Press any key to continue. ? If we remove the virus in MBR in the usual way, all the data in the password area will be lost.
Feeling:
I think many computer users turn pale when they hear "computer virus". Some of them do suffer, but most of them are afraid of themselves because of exaggerated hearsay. Not only fear, but also wallet damage (the trap of businessmen).
The harm of viruses to computers is well known, ranging from affecting the speed of machines to destroying files or causing crashes. In order to facilitate the maintenance of the computer at any time, it is necessary to prepare tools, such as clean dos startup disk or windows98 startup disk, as well as anti-virus and disk tool software to prevent the system from being infected with viruses or the hard disk from starting. In addition, drivers of various accessories should be prepared, such as CD-ROM drive, sound card, video card and modem. Cleaning discs and cleaning solutions for floppy disks and CD-ROM drives should also be kept in stock.