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.
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.
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.
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.
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.
