What are the types of viruses?

In the category of malicious code, computer viruses and worms are more destructive because they can replicate and infect remote systems. Computer viruses can usually be divided into the following categories:

Boot zone computer virus

File computer virus

Composite computer virus

macro virus

Troy/Trojan horse

insect

Types and production skills of other computer virus/malicious program codes

-

Boot zone computer virus

In the mid-1990s, the most popular computer virus was boot sector virus, which mainly spread through floppy disks in the environment of 16-bit disk operating system (DOS). Boot zone virus can infect the boot zone in floppy disks and hard disks, and it can also infect the main boot zone (MBR) in users' hard disks. Once the computer is poisoned, every floppy disk read by the infected computer will be infected.

The spread mode of computer virus in boot area is as follows: it is hidden in the disk, and the computer virus already exists in the memory before the system file is started. In this way, the computer virus can completely control the DOS interrupt function, thus spreading and destroying the virus. Boot zone viruses designed to run on DOS or Windows3. 1 cannot spread on new computer operating systems, so such computer viruses are rare.

Typical example:

Michelangelo is a boot zone virus. It will infect the MBR of the disk and hard disk in the boot area. When this computer virus resides in memory, it will infect all disks that are reading and not protected by writing. In addition, Michelangelo will delete all files on the infected computer on March 6.

File computer virus

File-based computer viruses, also known as parasitic viruses, usually infect executable files. Exe), but some will infect other executable files, such as DLL, SCR, etc ... Every time an infected file is executed, a computer virus will attack: the computer virus will copy itself to other executable files and continue to execute the original program to avoid being noticed by users.

Typical example:

CIH can be infected. EXE file, and caused serious damage on 26th of each month. On the 26th of every month, this pc virus will try to overwrite some random data on the system hard disk, so that the hard disk cannot read the original data. In addition, this virus will try to destroy the data in FlashBIOS.

Composite computer virus

Compound computer virus has the dual characteristics of boot zone virus and file virus.

macro virus

Unlike other computer viruses, macro viruses attack data files instead of program files.

Macro virus is specifically aimed at specific application software and can infect macro instructions attached to some application software. It can be easily spread through email attachments, floppy disks, file downloads and group software (such as MicrosoftWord and Excel). Macro viruses are written in programming languages, such as VisualBasic or CorelDraw, which are easy to master. Macro virus was first discovered in 1995, and soon became the most common computer virus.

Typical example:

Computer virus JulyKiller spreads in MSWord97 file through VB macro. Once an infected file is opened, the virus first infects the * * * template (normal.dot), causing other opened files to be infected one by one. This computer virus is very destructive. If the month is July, this virus will delete all files of c:\.

Troy/Trojan horse

Trojan horse or Trojan horse is a seemingly legal program, but in fact it will carry out some vicious and improper activities when it is executed. Trojan can be used as a hacking tool to steal users' password data or destroy programs or data on the hard disk. Unlike computer viruses, Trojan does not copy itself. Its communication skill is usually to trick computer users into implanting Trojan horses into their computers, for example, through game attachments in emails.