What are the types of computer viruses?

According to the method of computer virus attributes, computer viruses can be classified according to the following attributes.

First, according to the media where the virus exists:

1, network virus-spread executable files in infected networks through computer networks.

2. files infected with viruses in the computer (such as com, EXE, DOC, etc.). ).

3. Bootable virus-system boot sector (MBR) that infects boot sector and hard disk.

Second, according to the division of virus transmission channels:

1, resident virus-This virus infects a computer and puts the resident part of its own memory in RAM. This part of the program is linked to system calls, merged into the operating system, and is active until it is shut down or restarted.

2. Non-resident virus-This virus will not infect the computer memory when activated. Some viruses will leave a small part in memory, but they will not spread through this part. Such viruses are also classified as non-resident viruses.

Third, according to the destruction ability:

1, harmless-there is no other impact on the system except reducing the available disk space during infection.

2. Harmless-this virus will only reduce memory, display images, make sounds, etc.

3. Danger-This virus will cause serious errors in the operation of the computer system.

4, very dangerous-this kind of virus deletes programs, destroys data, and clears the system memory area and important information in the operating system.

Fourth, according to the algorithm:

1, COMpanion virus-this kind of virus does not change the file itself, but generates the companion of the EXE file according to the algorithm, with the same name and different extensions (com), such as XCOPY. EXE is accompanied by XCOPY-COM. When a virus writes itself to a COM file, it does not change the EXE file. When DOS loads a file, the satellite is executed first, and then the satellite loads and executes the original EXE file.

2, "worm" virus-spread through the computer network, without changing the file and data information, using the network to spread from the memory of one machine to the memory of other machines, and the computer sends its own virus through the network. Sometimes they exist in the system and generally do not occupy other resources except memory.

3. Parasitic viruses-Except companion viruses and worms, other viruses can be called parasitic viruses. They are attached to the boot sector or file of the system and spread through the functions of the system. According to their different algorithms, they can be subdivided into the following categories.

4, practice the virus, the virus itself contains errors, can not spread well, for example, some viruses are in the debugging stage.

5, stealth viruses, they generally do not directly modify the DOS interrupt and sector data, but modify the DOS interior through device technology and file buffer, so it is difficult to see the resources and adopt more advanced technology. Use the free data area of DOS to work.

6. Mutant virus (also known as ghost virus), which uses a complex algorithm to make each copy of itself have different content and length. Their general practice is a decoding algorithm, which mixes irrelevant instructions and changed virus bodies.

Verb (short for verb) is destructive.

1, benign virus

2. malignant viruses

3. Extremely malignant virus

4. Catastrophic virus.

Sixth, the mode of infection.

1, the boot zone virus mainly spreads in the operating system through floppy disks, infects the boot zone, spreads to the hard disk, and can infect the "master boot record" in the hard disk.

2. File virus is a file infected person, also known as "parasitic virus". It runs in COMputer memory and usually infects files with extensions of com, EXE and SYS.

3. Mixed virus has the characteristics of both boot virus and file virus.

4. Macro virus refers to the macro code registered in Office documents by virus programs written in BASIC language. Macro viruses affect various operations on documents.

Seven. Connection mode

1, the source virus attacks the source program written in a high-level language, which is inserted before the source program is compiled and connected with the source program to form an executable file. There are so few source viruses that it is difficult to write.

2. Intrusive viruses can replace some modules or stack areas in normal programs by themselves. Therefore, this virus only attacks some specific programs and is highly targeted. In general, it is also difficult to find and remove.

3. Operating system viruses can add or replace some functions of the operating system with their own components. Because it directly infects the operating system, such viruses are also harmful.

4. The shell virus usually attaches to the beginning or end of the normal program, which is equivalent to adding a shell to the normal program. Most file viruses fall into this category.

Extended data:

In order to replicate itself, a virus must be able to run code and write to memory. Therefore, many viruses attach themselves to legitimate executable files. If the user tries to run the executable file, the virus has a chance to run. According to the behavior of the runtime, viruses can be divided into two categories.

Non-resident viruses will immediately look for other hosts and wait for infection, and then give control to the infected application. Resident viruses will not look for other hosts when they run. Instead, the resident virus loads itself into memory and gives control to the host. Viruses run in the background, waiting for opportunities to infect other targets.

Resident viruses contain replication modules, which are similar to non-resident viruses. The replication module will not be called by the search module residing in the virus. When the virus runs, it will load the copy module into memory and ensure that the copy module will be called when the operating system runs a specific operation.

For example, when the operating system runs other files, the copy module will be called. In this case, all files that can be run will be infected. Resident viruses are sometimes divided into fast-infected people and slow-infected people. Rapidly infected people will try to infect as many files as possible.

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