Wednesday, 2 March 2011

Different Types of Computer Viruses. What is Viruses?

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Different Types of Computer Viruses. What is Viruses?


  What is a Computer Virus ?
A potentially damaging computer programme capable of reproducing itself causing great harm to files or other programs without permission or knowledge of the user.
                                                              Virus 
A program that when run, has the ability to self-replicate by infecting other programs and files on your computer. These programs can have many effects ranging from wiping your hard drive, displaying a joke in a small box, or doing nothing at all except to replicate itself. These types of infections tend to be localized to your computer and not have the ability to spread to another computer on their own. The word virus has incorrectly become a general term that encompasses trojans, worms, and viruses.
1) Boot Sector Virus :- Boot sector viruses infect either the master boot record of the hard 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 disk or 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-protected disk accessed by this system will become infected. Examples of boot- sector viruses are Michelangelo and Stoned.
2) File or Program Viruses :- Some files/programs, when executed, load the virus in the memory and perform predefined functions to infect the system. They infect program files with extensions like .EXE, .COM, .BIN, .DRV and .SYS .
Some common file viruses are Sunday, 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, files at the same time. When the virus attaches to the boot sector, it will in turn affect the system’s files, and when the virus attaches to 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, discovered by Fridrik Skulason in October 1989.
Other examples are Invader, Flip, etc.
4) Stealth Viruses :-These viruses are stealthy in nature means it uses various methods 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 program a clean image of the file or boot sector.
5) Polymorphic Viruses :- Polymorphic viruses have the ability to mutate implying that they change the viral code known as 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 the application 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-known examples are Concept Virus and Melissa Worm.
7) Rootkit Virus:- A rootkit virus is an undetectable virus which attempts to allow someone to gain control of a computer system. The term rootkit comes from the linux administrator root user. These viruses are usually installed by trojans and are normally disguised as operating system files.
8) Logic Bombs/Time Bombs:- These are viruses which are programmed to initiate at a specific date or when a specific event occurs. Some examples are a virus which deletes your photos on Halloween, or a virus which deletes a database table if a certain employee gets fired.
 Malware – Malware is programming or files that are developed for the purpose of doing harm. Thus, malware includes computer viruses, worms, Trojan horses, spyware, hijackers, and certain type of adware.
 Backdoor- A program that allows a remote user to execute commands and tasks on your computer without your permission. These types of programs are typically used to launch attacks on other computers, distribute copyrighted software or media, or hack other computers.
Hijackers- A program that attempts to hijack certain Internet functions like redirecting your start page to the hijacker’s own start page, redirecting search queries to a undesired search engine, or replace search results from popular search engines with their own information.
Spyware- A program that monitors your activity or information on your computer and sends that information to a remote computer without your Knowledge.
Adware- A program that generates popups on your computer or displays advertisements. It is important to note that not all adware programs are necessarily considered malware.There are many legitimate programs that are given for free that display ads in their programs in order to generate revenue. As long as this information is provided up front then they are generally not considered malware.
Dialler - A program that typically dials a premium rate number that has per minute charges over and above the typical call charge. These calls are with the intent of gaining access to pornographic material.
Trojan- A program that has been designed to appear innocent but has been intentionally designed to cause some malicious activity or to provide a backdoor to your system.
Worm- A program that when run, has the ability to spread to other computers on its own using either mass-mailing techniques to email addresses found on your computer or by using the Internet to infect a remote computer using known security holes.

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