Computer Virus - An Introduction
A computer virus is a program which enters and operates
illegally into a system with the purpose of disturbing its
operation. Computer virus has the capacity to replicate, which it
uses to proliferate in a machine and affect its software and
hardware.
Sources of infection. Computer viruses can spread through any
computer compatible mode you can think of. Emails, messenger
messages, attachments, files, pen drives, floppies, CDs or any file
generated from a virus affected system. As soon as the viral code
executes in your machine, the virus activates, starts replicating
and takes over your system completely.
Types of computer virus. Based upon the areas in your computer
that these viruses attack, they are of the following varieties:
- File infector viruses. These are quite common viruses
which tag themselves to the files executing in your machine. These
viruses can be attached generally with any number of system files
having extensions, .EXE, .COM, .SYS, .PRG, .OVL, and .MNU. As these
files run on your machine, viruses get activated and start
duplicating. Eventually, viruses spread in the whole of your
machine. Some file infector viruses may stay in your system’s
memory and keep infecting files from even there.
- Boot sector viruses. Also called as bimodal viruses, they
attach themselves to DOS boot sector and start affecting the coding
of some system files. Their variant Master Boot Record (MBR)
viruses adhere themselves to MBR sector on your machine’s hard
disk. Once infected booting happens, the virus lodges in your
system’s memory and starts affecting the other data storage media
such as CD, floppies and pen drives, as you save data from your
infected system on to these. Now, these media when inserted in
another computer will infect it as well, if it does not have
antivirus installed in it. These days however, with the floppies
becoming obsolete, these viruses are also reduced to
insignificance.
- Macro viruses. They are the commonest, simplest and the
easiest to handle of all the computer viruses. Usually they affect
MS Office files such as MS Word files, Excel sheets, Access
databases, and PowerPoint. Macro viruses are coded in Visual Basic
(VB) and blight your system when the application with which they
are associated is running. An example of macro virus impact is
insertion of some data in the spreadsheet your system processes.
Melissa.A and Bablas. Pc is a couple of common macro viruses.
- Network viruses. As the name suggests, these viruses
originate from and affect computer networks such as LAN and WAN.
Network viruses defile any shared computer resources such as
folders, files, drives etc. These viruses keep spreading from one
system of an infected network to another. Nimda and SQLSlammer are
two examples of network viruses.
- Multi-partite viruses. Their nature is a mix of more than
one type of viruses and spread through infected media. For example,
viruses acting both as MBR virus as well as file infector
virus.
- Worms. These are viruses that can replicate themselves, are
sent via your computer’s network and use your machine’s memory to
execute. Worms however, proliferate as simple emails without
attachment. They cannot be spread as attachments.
Impact of computer viruses. Computer viruses may infect your
system at all levels, basic to complex. They may wipe, alter or
damage the data from your computer, some may go to the extent of
damaging your hard disk and you may need to reformat it. Some
viruses may slow down your system by using your computer’s memory
and hard disk space.
Combating computer virus. Installing registered version of a
reputed antivirus on your computer, generally keeps your system
fit. Antivirus removes the viruses it is able to detect on your
system and prohibits the others from entering. Needless to say,
keep your antivirus updated regularly.
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