There are various types of computer virus that can be classified by their origins, techniques of attack, modes of spreading, forms of infections, hiding locations and the kind of damage caused. This article provides information about these types.
Resident Virus
These virus hide permanently in the RAM of the computer. From there, they control and intercept all sorts of operations carried out by the system thereby infecting files and programs which are opened, closed, copied, pasted etc. Examples of resident virus include Randex, Meve and MrKlunky.
Boot Sector Virus
Boot sector virus hide themselves in the boot sectors of either the removable bootable disks or the hard disk of the computer. In contrast to most other virus, these virus do not damage the files in the hard disk, but damage the hard disk itself. Examples of boot sector virus include Form, Michelangelo and Disk Killer.
Program virus
Program virus trigger off when the file (usually with extensions .bin, .com, .exe or .drv) carrying them is opened. Once active, these virus make copies of themselves and infect other programs on the computer. Examples of program virus include Sunday and Cascade.
Macro Virus
Macro virus write themselves into the source codes of common application programs such as Word or Excel. These virus infect templates of these documents and therefore every file that the user opens gets affected. Macro virus are platform-free since they are written in the language of the application and not of the operating system. When the application runs, it allows the macro virus to spread out amongst different operating systems. Examples of macro virus are Melissa A, Nuclear and Word Concept.
Polymorphic Virus
Polymorphic virus encrypt themselves in a distinct way (using unique algorithms and encryption codes) each time they infect a system. This renders it impossible for antivirus software to trace them by using string or signature search techniques (since they are dissimilar in each encryption) and also allows them to make scores of copies of themselves. Examples of polymorphic virus include Elkern, Marburg, Tuareg and Satan Bug.
Network Virus
Network virus rapidly spread through a Local Area Network (LAN) and sometimes through the Internet. When these virus infect a computer, they search through the network to attack their new potential prey. When they are finished infecting that computer, they move on to the next and the cycle repeats itself. The most dangerous network virus are Nimda and SQLSlammer.
The above description provides you comprehensive information about the different types of computer virus that may infect your computer. You should always install antivirus software on your computer to protect it from getting infected by these virus.
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