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What is virus? who can explain? Reward $2
Created by eng19342, 1658 days ago, 2112 views

What is virus? who can explain.
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brendaniel1658 days ago

A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce many thousands of identical copies of the original virus at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. But unlike still simpler infectious agents, viruses contain genes, which gives them the ability to mutate and evolve. Over 5,000 species of viruses have been discovered.

A computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) or infecting other computer programs by modifying them.Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive. When this replication succeeds, the affected areas are then said to be "infected" with a computer virus. The term "virus" is also commonly, but erroneously, used to refer to other types of malware. "Malware" encompasses computer viruses along with many other forms of malicious software, such as computer "worms", ransomware, trojan horses, keyloggers, rootkits, spyware, adware, malicious Browser Helper Object (BHOs) and other malicious software. The majority of active malware threats are actually trojan horse programs or computer worms rather than computer viruses.

Viruses often perform some type of harmful activity on infected host computers, such as acquisition of hard disk space or central processing unit (CPU) time, accessing private information (e.g., credit card numbers), corrupting data, displaying political or humorous messages on the user's screen, spamming their e-mail contacts, logging their keystrokes, or even rendering the computer useless. However, not all viruses carry a destructive "payload" or attempt to hide themselves—the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without user consent.

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Aravi1656 days ago

Hi @eng19342

Sorry, I think we have 2 different things called as virus

(A) A virus is a as per biological science :-

1) Nether living nor non living substance.

2) They all have dual face:-

a) non living source face which have a protein cover and core DNA / RNA structure.

b) When it infects it have living DNA / RNA structure that freely floats in host organism's cell. Covered with protein made outer cover.

3) It don't have cellular structure.

4) can undergo self-replicating/ mutation of its DNA / RNA within a second.

(B) A virus is a as per computer science :-

1) A self-replicating computer programs which infects host devices like computer or mobile.

2) It was first made in USA around 1950 to study the ability of computer program to exist like a biological virus.

3) It have more then 100 of classification based on how they infect computer to how to detect, etc,

Some commonly used definition based on type of virus:

Most Common Types of Viruses and Other Malicious Programs

1. Resident Viruses

This type of virus is a permanent which dwells in the RAM memory. From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.

Examples include: Randex, CMJ, Meve, and MrKlunky.

2. Multipartite Viruses

Multipartite viruses are distributed through infected media and usually hide in the memory. Gradually, the virus moves to the boot sector of the hard drive and infects executable files on the hard drive and later across the computer system.

3. Direct Action Viruses

The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that it is in and in directories that are specified in the AUTOEXEC.BAT file PATH. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.

4. Overwrite Viruses

Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected.

The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

Examples of this virus include: Way, Trj.Reboot, Trivial.88.D.

5. Boot Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.

The best way of avoiding boot viruses is to ensure that floppy disks are write-protected and never start your computer with an unknown floppy disk in the disk drive.

Examples of boot viruses include: Polyboot.B, AntiEXE.

6. Macro Virus

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one.

Examples of macro viruses: Relax, Melissa.A, Bablas, O97M/Y2K.

7. Directory Virus

Directory viruses change the paths that indicate the location of a file. By executing a program (file with the extension .EXE or .COM) which has been infected by a virus, you are unknowingly running the virus program, while the original file and program have been previously moved by the virus.

Once infected it becomes impossible to locate the original files.

8. Polymorphic Virus

Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system.

This makes it impossible for anti-viruses to find them using string or signature searches (because they are different in each encryption) and also enables them to create a large number of copies of themselves.

Examples include: Elkern, Marburg, Satan Bug, and Tuareg.

9. File Infectors

This type of virus infects programs or executable files (files with an .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belongs to this category, and can be classified depending on the actions that they carry out.

10. Encrypted Viruses

This type of viruses consists of encrypted malicious code, decrypted module. The viruses use encrypted code technique which make antivirus software hardly to detect them. The antivirus program usually can detect this type of viruses when they try spread by decrypted themselves.

11. Companion Viruses

Companion viruses can be considered file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they "accompany" the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident viruses) or act immediately by making copies of themselves (direct action viruses).

Some examples include: Stator, Asimov.1539, and Terrax.1069

12. Network Virus

Network viruses rapidly spread through a Local Network Area (LAN), and sometimes throughout the internet. Generally, network viruses multiply through shared resources, i.e., shared drives and folders. When the virus infects a computer, it searches through the network to attack its new potential prey. When the virus finishes infecting that computer, it moves on to the next and the cycle repeats itself.

The most dangerous network viruses are Nimda and SQLSlammer.

13. Nonresident Viruses

This type of viruses is similar to Resident Viruses by using replication of module. Besides that, Nonresident Viruses role as finder module which can infect to files when it found one (it will select one or more files to infect each time the module is executed).

14. Stealth Viruses

Stealth Viruses is some sort of viruses which try to trick anti-virus software by intercepting its requests to the operating system. It has ability to hide itself from some antivirus software programs. Therefore, some antivirus program cannot detect them.

15. Sparse Infectors

In order to spread widely, a virus must attempt to avoid detection. To minimize the probability of its being discovered a virus could use any number of different techniques. It might, for example, only infect every 20th time a file is executed; it might only infect files whose lengths are within narrowly defined ranges or whose names begin with letters in a certain range of the alphabet. There are many other possibilities.

16. Spacefiller (Cavity) Viruses

Many viruses take the easy way out when infecting files; they simply attach themselves to the end of the file and then change the start of the program so that it first points to the virus and then to the actual program code. Many viruses that do this also implement some stealth techniques so you don't see the increase in file length when the virus is active in memory.

A spacefiller (cavity) virus, on the other hand, attempts to be clever. Some program files, for a variety of reasons, have empty space inside of them. This empty space can be used to house virus code. A spacefiller virus attempts to install itself in this empty space while not damaging the actual program itself. An advantage of this is that the virus then does not increase the length of the program and can avoid the need for some stealth techniques. The Lehigh virus was an early example of a spacefiller virus.

17. FAT Virus

The file allocation table or FAT is the part of a disk used to connect information and is a vital part of the normal functioning of the computer.

This type of virus attack can be especially dangerous, by preventing access to certain sections of the disk where important files are stored. Damage caused can result in information losses from individual files or even entire directories.

18. Worms

A worm is technically not a virus, but a program very similar to a virus; it has the ability to self-replicate, and can lead to negative effects on your system and most importantly they are detected and eliminated by antiviruses.

Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.

19. Trojans or Trojan Horses

Another unsavory breed of malicious code (not a virus as well) are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms.

20. Logic Bombs

They are not considered viruses because they do not replicate. They are not even programs in their own right but rather camouflaged segments of other programs.

Their objective is to destroy data on the computer once certain conditions have been met. Logic bombs go undetected until launched, and the results can be destructive.


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selected1632 days ago

A virus is something nasty that spreads by direct contact or another medium, se.g. air or network connection. Depends if it's biological or computers.

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nihal291632 days ago

hi @eng19342
a piece of code which is capable of copying itself and typically has a detrimental effect, such as corrupting the system or destroying data.
a computer virus can also execute instructions that cause harm. For this reason, computer viruses affect security. They are part of malware. Very often, the term is also used for other kinds of malware, such as trojan horses and worms.
a virus is created by persons for personal profit . remember some virus removing experts? they know how the particular virus work and how to stop it .

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Final_Vers1632 days ago

A virus is a small infectious agent that replicates only inside the living cells of other organisms.

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capybara1629 days ago

A computer virus is similar in many respects to a human virus.

Wether it's a computer code, or living cells, when a system get infected the results are about the same. The idea is all about self-replication.

In humans it's at the cellular level, and in many cases goes away in time when white blood cells and antibodies eventually kill it.

In computers, the virus is a bit of self-replicating code that can cause problems at all levels, from the annoying to devestating.

So, just like when you get your flu shot every year, make sure you have a stong antivirus program, and keep it updated.

Good Luck.

Caplain the Capybara.

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zeos1629 days ago

Компьютерный вирус является разновидностью программы вредоносного программного обеспечения (вредоносных программ), которые при выполнении, воспроизводят (копируют) свой собственный исходный код или заражают другие компьютерные программы, модифицируя их. Заражая компьютерные программы, могут включать также, файлы данных, или "загрузочный" сектор жесткого диска. Если репликация прошла успешно,то можно сказать, что программы заражены компьютерным вирусом. Термин "вирус" тоже часто, но ошибочно, используется для обозначения других типов вредоносных программ. "Вредоносные программы" включают в себя компьютерные вирусы, наряду со многими другими формами вредоносного программного обеспечения, такого как компьютерные "черви", программы-вымогатели, трояны, клавиатурные шпионы, руткиты, шпионские программы, рекламное ПО, вредоносные объекты модуля поддержки броузера и другие вредоносные программы. Большинство активных вредоносных программ на самом деле являются компьютерными программами или компьютерными червями , а не компьютерными вирусами.

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medfen4ik1629 days ago

what is the virus?
please name them or what happen with the system ?

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