Describe the types of viruses.

Computer Virus

Types of viruses

The names of two species of virus in general are particularly noteworthy. Two types are Trojan horse and worm virus-

• Trojan horse virus: This type of virus encourages the computer user to follow the message with some interesting message. By responding to the Trojan virus's call, the computer user is in immediate danger.

• Worm virus: This type of virus gets into the computer like a malicious insect along with any file. Then it attacks the special files of the computer by making automatic copies and enters and disrupts the normal functioning of the computer. Computer viruses can be mainly divided into two categories on the basis of their destructive effect, like:


(i) Program Viruses
(ii) Boot sector virus.


Program virus: This type of virus adds virus code to the first or last part of the executable file. In this case the number of bytes of the executable file shows more or less than the actual number. In this case, some common words can be noted as extensions at the end of the executable file, such as exe, com, ovl, drv sys etc.


Program virus activities can be divided into two categories, namely--

(a) Direct File Infected Viruses
(b) Indirect file infected viruses.


Boot Sector Virus: This type of virus directly modifies the boot sector of the floppy or hard disk and becomes part of the operating system. The virus first loads into memory. It then replaces the code located in the boot sector and replaces the boot sector with the virus code. When a computer infected with such a virus is turned on, the virus code is first stored in memory and disrupts the normal booting of the computer.


In terms of time, viruses can be divided into three categories:

(i) Instant acting viruses : Attacks of such viruses cause immediate downtime of the computer. Boot sector viruses cause such immediate problems.

(ii) Hierarchical virus : After attacking the computer, this type of virus gradually dominates the computer system and at one time paralyzes the normal functioning of the computer.


(iii) Time Bomb Virus : This type of virus hides in the computer for a long period of time. Then come alive on a certain day and damage the computer, such as Jerusalem B virus, CIH virus.