Types of Computer Virus

Types of viruses :-

The different types of viruses areas follows-

1) Boot Sector Virus :- Boot sector viruses infect either the master boot record of thehard disk or the floppy drive.The boot record program responsible for the booting of operating system is replaced by the virus. The virus either copies the master boot program to another part of the hard diskor overwrites it. They infect a computer when it boots up or when it accesses the infected floppy disk in the floppy drive. i.e. Once a system is infected with a boot-sector virus,any non-write-prote ­cted disk accessed by this system will become infected.
Examples of boot- sector viruses are Michelangelo andStoned.

2) File or Program Viruses :- Some files/ ­programs, when executed, load the virus in the memory and perform predefined functions to infectthe system. They infect program files with extensionslike .EXE, .COM, .BIN,.DRV and.SYS .
Some common file viruses areSunday, Cascade.

3) Multipartite Viruses :- A multipartite virus is a computer virus that infects multiple different target platforms, and remains recursively infective in each target. It attempts to attack both the boot sector and the executable, or programs, filesat the same time. When the virus attaches to the boot sector, it will in turn affect the system’s files, andwhen the virus attachesto the files, it will in turn infect the boot sector.
This type of virus can re-infect a system over and over again if all parts of the virus are not eradicated.
Ghostball was the first multipartite virus, discoveredby Fridrik Skulason in October 1989.
Other examples are Invader,Flip, etc.

4) Stealth Viruses :- These viruses are stealthy in nature means it uses variousmethods for hiding themselves to avoid detection. They sometimes remove themselves from the memory temporarily to avoid detection by antivirus. They are somewhat difficult to detect. When an antivirus program tries to detect the virus, the stealth virus feeds the antivirus programaclean image of the file or bootsector.

5) Polymorphic Viruses :- Polymorphic viruses have the ability to mutate implying that they change the viral code knownas the signature each time they spread or infect. Thus an antivirus program which is scanning for specific virus codes unable to detect it's presense.

6) Macro Viruses :- A macro virus is a computer virus that"infects" a Microsoft Word or similar application and causes a sequence of actions to be performed automatically when theapplication is started or something else triggers it. Macro viruses tend to be surprising but relatively harmless.A macro virus is often spread as an e-mail virus.Well-know ­n examples are Concept Virus and Melissa Worm.