Common computer viruses and types of computer viruses

Source: Internet
Author: User
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What are the common computer viruses?

According to the virus existence media, the virus can divide into the network virus, the file virus, the boot type virus. Network virus spreads the executable file in the network through the computer network, file viruses infect files on your computer (such as: Com,exe,doc, etc.), boot-type virus infection boot sector (boot) and the system Boot sector (MBR) of the hard disk, and mixed types of these three cases, such as: Multi-virus ( File and boot type) infected files and boot sector targets, such viruses often have complex algorithms that use unconventional methods to invade the system while using encryption and distortion algorithms.

According to the method of virus transmission can be divided into resident virus and non-resident virus, resident virus infected with the computer, its own memory resident part in memory (RAM), this part of the program Hook system calls and merged into the operating system, he is in the active state, Until shutdown or reboot. Non-resident viruses do not infect computer memory when they are given an opportunity to activate, and some viruses keep a small portion of memory, but they are not transmitted through this part of the virus, which is also classified as a non-resident virus.

Harmless type: In addition to reducing the free space of the disk in case of infection, there is no other effect on the system.

No danger: This type of virus is only to reduce memory, display images, sound and similar audio.

Dangerous type: This type of virus causes serious errors in computer system operation.

Very dangerous: This kind of virus deletes the program, destroys the data, clears the system memory area and the important information in the operating system. The damage to the system by these viruses is not a risky call in its own algorithm, but an unpredictable and catastrophic disruption when they are transmitted. Errors caused by other programs created by the virus can also damage files and sectors, which are also divided by the destructive power they cause. Harmless viruses can also cause damage to new versions of DOS, Windows, and other operating systems. For example, in an earlier virus, there was a "Denzuk" virus that worked well on a 360K disk without causing any damage, but could cause a lot of data loss on later high-density floppy disks

Accompanying virus, this kind of virus does not change the file itself, they generate the EXE file companion according to the algorithm, have the same name and different extension (COM), for example: XCOPY.EXE the companion body is xcopy-com. The virus writes itself to COM file does not change EXE file, when the DOS load file, the accompanying body priority is executed, and then by the accompanying body load executes the original EXE file.

Worm virus, spread through computer network, do not change file and information information, use the network from a machine's memory to spread to other machine's memory, compute network address, send its own virus through network. Sometimes they exist in the system, except that the memory does not occupy other resources.

Parasitic viruses, in addition to the accompanying and "worm" type, other viruses can be called parasitic viruses, they are attached to the system's boot sector or files, through the function of the system to propagate, according to its different algorithms can be divided into: exercise-type virus, the virus itself contains errors, can not be very good transmission, such as some viruses in the debugging phase.

Secretive viruses they generally do not directly modify DOS interrupts and sector data, but through the device technology and file buffer, such as DOS internal modification, not easy to see resources, using more advanced technology. Work with DOS-free data areas.

Variant viruses (also known as phantom viruses) use a complex algorithm to make each transmission a different content and length. Their general approach is a decoding algorithm with a mixed-independent instruction and a changed virus body.

What kinds of computer viruses are there?

Boot area computer virus

In the 90 's, the most popular computer virus is the boot area viruses, mainly through the floppy disk in the 16-bit disk operating system (DOS) environment spread. The boot zone virus infects the boot area and hard disk within the floppy disk, and can also infect the primary boot area (MBR) within the user's hard disk. Once the computer is poisoned, every floppy disk that has been read by the infected computer will be infected.

Boot area computer viruses are so spread: hidden inside the disk, computer viruses have resided in memory before the system files started. As a result, computer viruses can fully control the DOS interrupt function for virus propagation and destruction activities. Those that are designed to perform on DOS or Windows3.1 are not able to spread on new computer operating systems, so this type of computer virus is already rare.

File type computer virus

File-type computer viruses, also known as parasitic viruses, typically infect execution files (. EXE), but some can infect other executable files, such as DLL,SCR, etc. ... Every time an infected file is executed, a computer virus occurs: The computer virus copies itself to other executables and continues to execute the original program to avoid being perceived by the user.

Complex computer virus

Complex computer virus has the dual characteristics of boot area virus and file viruses.

Macro virus

Macro viruses are specifically designed for specific applications that can infect macro directives that are attached to some application software, and can be easily disseminated via e-mail 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, and these are easy to master programming languages. Macro viruses were first discovered in 1995 and have become the most common computer viruses in the near future.

Troy/Trojan Horse

Trojan or Trojan Horse is a seemingly legitimate procedure, but in fact it carries out some vicious and improper activities when executed. Trojan can be used as a hacker tool to steal user's password information or damage the program or data on the hard drive. The difference with computer viruses is that Troy does not replicate itself. Its communication techniques are often used to trick computer users into putting Trojan horses into computers, such as the attachment of games on email.

Worm virus

Worms are another program that can replicate itself and spread through the web. Unlike computer viruses, which typically focus on infecting other programs, worms are focused on using the web to spread. By definition, computer viruses and worms are not compatible. With the popularity of the Internet, worms use e-mail systems to replicate, such as hiding themselves in attachments and emailing them to multiple users in a short time. Some worms, such as codered, are more likely to exploit software vulnerabilities to spread and destroy.

Other computer viruses/malicious code

A malicious program usually refers to a program written with the intent of the attack. These threats can be grouped into two categories: threats that require host programs and threats that are independent of each other. The former is essentially a program fragment that is not independent of a real application, utility, or System program, which is a self-contained program that can be scheduled and run by the operating system. You can also divide these software threats into tasks that do not replicate and replicate.

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