Computer virus is man-made software to destroy the computer which causes hindrance in the progress of work. Being man-made, they are programmed in various ways. It means there are different types of virus program which shows different results when it infects a certain unit. However one thing should be made clear that it only affects the software not the hardware of computer. Different types of viruses affects according to the program through which it launch on to the computer system either from a particular program, file, disk, floppy or USB.
According to the launching mechanism there are three different types of viruses as;
- Hard communication
In this category a virus attack when an outer hard device is attached to the computer system like USB, floppy, smart memory card or CDs, etc. Many viruses come under this category for example;
Boot Virus infects the hard disk and attaches itself to the start menu to boot automatically when the system runs. These types of boot viruses are polyboot B and anti exe. It is better to be certain about the absence of any kind of virus before boot the floppy. Boot virus enters into the system through USB, disk, card, etc.
- File Virus
This category has a large number of viruses each behave differently and in a unique way.
- FAT Virus is the basic system infection virus in which the disk having the allocation guide is infected. This is the core of system from where different programs get command to run. This FAT virus places hindrance in approaching the part to start the program which appears in the form loss of important information.
- Companion Virus is the consort file. In this way they behave according to the original file and execute with it. It remains inactive and start run when the file is open examples are Stator, Asimov 153 and Terrax 1069
- Polymorphic Virus starts encrypting the file in a tricky way by changing the algorithm each copy it makes. This nature if polymorphic virus makes difficult to detects its presence. Examples are Elkern, Marburg, Satan bug, Taureg.
- Macro virus replicate itself speedily just by one click as single action like relax, Melissa A, bablas and O97M/Y2K
- Overwrite virus contaminated the files which have information and make the files useless for the use examples are way, trj reboot, trivial 88D.
- Soft communication like internet surfing, email can also launch virus onto the computer system while receiving these types of viruses one remains ignorant of their presence before its execution.
- Directory Virus misguides from the right location and distracts the information. This type of virus infects the system through email attachment and being ignorant you download the attachment as useful information or opening a website during netsurfing which would be virus infected and as a result receive virus in your system which get store in the memory of computer. Opening the download attachment or file start spreading its infection and contaminated the host.
- Direct Action Virus starts replication and enters into the root directory of the system and gets its hold. Whenever system boot this batch file activates in auto exec bat file.
Networking is very common now-a-days on small and big scale. It also makes easy for the virus to spread the infection on a large scale. This category include a very famous virus like
- Logic Bomb or commonly known as time bomb is very famous as it activates on the exact date when it take birth. This virus remand dormant till the date of execution arrives. It wakes up and start destroying every computer comes in its path of launching. The only cure of this virus is not to remain in touch with the network every time or at least close the system most of the time on this date.