What Is Computer Virus? Types Of Computer Virus

What Is Computer Virus ?

The virus commonly heard threat to information and system security is the VIRUS.( Vital Information Resources Under Siege).
What Is Computer Virus? Types Of Computer Virus
 Computer Virus 
  It is a program that can affect other Previously existing programs and thereby it creates trouble in its smooth execution. It also infects other programs by modifying them. By modification we mean inclusion of a copy of the virus program into an already existing program which in turns infects other previously unaffected programs within the system.

 The key feature of an any computers virus it is unique capability to replicate itself which takes place by the modification of an existing program file with a copy of the virus itself.
 Once a virus is in execution within a system, it can damage information by erasing existing files and programs from the system.

Boot Sector Virus :

The boot sector is the program that is loaded as soon as an end user switches on the CPU of a system. Boot sector virus attacks the boot record of a system. The boot sector virus damages a system in the following ways:

1. It over writes the existing and original boot code of a computer system with its own virus affected code.

2. It relocates the actual information which was present in the boot sector to another sector on the hard disk.

3. Subsequently it marks that particular sector on the disk which is popularly known as a bad sector on the hard disk.

4. With increase in the number of bad sector not only a particular hard disk is damaged but also there is a high probability of the hard disk going out of order permanently.

File Infecting Virus :

The file Infecting virus as the name implies attacks and damages most of the executable files within a computer system. Generally the extension of file Infecting virus of EXE or. COM . The file Infecting virus damage the system in the following ways:

1. The virus multiplies itself by getting attached with existing uninfected executable programs within a system.

2. After this attachment the unaffected executable program is modified by this particular virus.

3. When an end-user unknowingly executes those programs, the virus becomes active.

Polymorphic Virus :

The word ‘poly’ means ‘many’ and the word ‘Morph’ means ‘forms’. Therefore polymorphic viruses are those viruses with more than one form within a system. The polymorphic virus damages the system in the following ways :

1. Detection of polymorphic virus is very difficult because one copy of the polymorphic virus looks different from another.

 2. Polymorphic virus use encryption Technology for its  successful multiplication.

3. During execution just the encrypted virus decrypted and then it is executed. The decryption of the encrypted part of the polymorphic virus is done by virus decryption Routine.

Stealth Virus :

This virus as the name implies conceals its presence from an end-user. The stealth virus damages the system in the following ways:

1. The Stealth virus affects a particular file and if some other program tries to access that file the stealth virus goes back to its unchanged form.

2. As a consequence the end-user does not find any symptom of the virus in the system.

In Oder to make a system free from stealth virus it always advisable to boot a system from unknown Virus free CD/VDV. if this happens the virus cannot exercise its control and then when an antivirus software is executed the virus is easily under arrest.

Multipartite virus :

Multipartite virus is perhaps the most dangerous virus type available. Multipartite virus can affect a system in more than one ways simultaneously as a consequence it often proves  fatal  to a system. The multipartite virus damage the system in the following ways :

1. Multipartite virus can affect the boot sectors as well as the executable files present within a system all at once.

2. Multipartite virus processes the features of polymorphic virus as well as stealth virus and as a consequence it is very difficult to detect them.

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