Common types of Computer Virus

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August 16,2012
Computer Viruses are of various types. Since the mission of the creator of these viruses is malicious and injurious to computer systems a clear knowledge of the Common types of Computer virus is necessary to avert falling a victim. Viruses are coded program or software with the intent of gaining access to a computer machine and performing certain predetermine activities which ranges from collecting confidential information, erasing computer files and programs and for other ulterior motive. The classification of types of computer viruses should not be audacious as there are many literatures with various schools of thought as per their classification. For the sake of simplicity, we shall be looking at two broad categories:
Those that can be executed by the operating system and those that rely on applications before they can get executed.

1. Boot sector Virus: As the name implies, this virus main target are the programs stored in the floppy and hard disk. This can corrupt the programs that make the computer machine to boot or come on; hence the system is completely grounded or crashed. Their task is to run or get executed as the system boot thereby taking control of the entire system. Example of these types of viruses are Polyboot.B, AntiEXE
2. Resident Virus: This type of Virus resides in the Ram of the computer. From this point it can corrupt, interrupt and control other operations in the system. Examples are Mr Klunky, CMJ, Relex-D , Meve etc.
3. Macro Virus: This is one of the most recent types of computer virus that utilises application software macro programming script for the malicious purpose for which it was created. Unlike other virus it does not affect programs, it affects documents. This is usually done by the virus code modifying original instructions on these documents in order to take control of the entire PC. Microsoft word document files are the most infected by this virus. Examples are Relax, Bablas etc
4. File Infectors: Exe or .com files are the target of this virus. The virus can corrupt, change or delete these files each time the program is run. Examples are Cascade and Cleevix.
5. Network Virus: This type of computer virus spread via the internet and through the local network of computers. As long as the computer is in the network it will be infected if not protected. Example is Nimda virus.
6. Logic Bomb: This is the type of coded software that will not operate until certain conditions are met. They are codes that are embedded in the operating system software on the computer. It can be there for a very long time without doing any harm until that particular instruction coded is carried out by the system operator or a specific period of time in the year. At that time the script is activated alongside the normal operation of the computer to execute the purpose for which it was written.
7. Companion Virus: This virus is written in close affinity with existing files in such a way that each time that file is executed it gets activated alongside. They are like the direct action or resident virus. They can wait until that coded action is carried out by the existing files. As they are activated and replicate themselves, they can corrupt and even replace existing file. Example : Asimov virus.
8. Overwrite Viruses: This type of virus deletes or corrupts the files that it infects in such a way that they are rendered partially or totally useless. They can completely lose their original content.The only remedy in removing the virus is to delete files affected completely. Example: Trivial.88.D
9. Fat Virus: The target of this virus is one of the most important part of the computer machine, the section responsible for information dessemination such as the files location directory, amount of space available on the hard disk, unused space etc. The virus can modify the direction or the instruction on this directory in such a way that computer operator will run the virus programme unknowingly while the original files and programs would have been moved or deleted
10. Worms: These are software program that has the ability to replicate themselves like virus with great damaging effects on the computer. It uses computer network to spread when there is security lapses e.g. ExploreZip worm.
11. Trojan Horses: Unlike computer viruses, Trojan horses do not replicate themselves but they are very dangerous and injurious. They have the ability of disguising as useful important software from the surface but can destroy the security and defence system of the computer machine thereby creating loopholes for the malicious intent of the designer to be carried out. Trojans are known for creating access for the invasion of Rootkit virus which disguise as operating system files.
12. Polymorphic Virus: This is a very deceptive type of virus. Apart from the fact that it possesses the ability to replicate itself very fast, in that same process it changes its digital signature. It guards itself with an encryption algorithm that changes its codes under prescribed conditions. So it becomes very difficult to detect it by a less sophisticated anti-virus software. Example is 1260 virus.
13. Multipartite Virus: This type of virus exploits every possible means to spread or replicate itself. In other words it can operate and spread in multiple ways using the operating system and files. The strength the virus exacts also depends on the type of programs and files install on a computer machine.
14. Browser Hijacker: This type of virus can infect a browser by modifying and redirecting an operator completely to sites not intended for malicious gains. Such viruses can later infect other parts of the operating system and files through attachments and other materials downloaded. Example: Coolwebsearch etc.
15. Web Scripting Virus: Websites uses various codes to enable it display certain features such as the ability to play an online video, music, applications etc. A virus can exploit this means to infect and gain control over the entire system.

The list of the Common types of Computer viruse goes on as it is a continuous discovery. Once an existing virus is detected and dealt with, malicious virus designers will always go back to the drawing board to device means of modifying existing ones and creating new ones. The best means to forestal becoming a victim is to be on the guard by installing appropriate anti-virus software.

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