About different types of computer virus.

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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.
Types of viruses :-
The different types of viruses are as
follows-
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.
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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.
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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.
If you use a computer, read the
newspaper, or watch the news, you will
know about computer viruses or other
malware. These are those malicious
programs that once they infect your
machine will start causing havoc on
your computer. What many people do
not know is that there are many
different types of infections that are
categorized in the general category of
Malware.
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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.
This article will focus on those malware
that are considered viruses, trojans,
worms, and viruses, though this
information can be used to remove the
other types of malware as well. We will
not go into specific details about any one
particular infection, but rather provide a
broad overview of how these infections
can be removed. For the most part these
instructions should allow you to remove a
good deal of infections, but there are
some that need special steps to be
removed and these won’t be covered
under this tutorial.
Before we continue it is important to
understand the generic malware terms
that you will be reading about.
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.
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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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