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 The Difference Between a Virus, Worm and Trojan Horse

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Join date : 2007-11-08
Age : 48

PostSubject: The Difference Between a Virus, Worm and Trojan Horse   Sun Dec 16, 2007 9:59 pm

The Difference Between a Virus, Worm and Trojan Horse

The most common blunder people make when the topic of a computer virus arises is to refer
to a worm or
Trojan horse as
a virus. While the
words Trojan, worm and virus are often used interchangeably, they are not
the same. Viruses, worms and Trojan Horses are all malicious
programs that can
cause damage to your
, but there are differences among the three, and knowing those
differences can help you to better protect your computer from their often
damaging effects.

A computer virus
attaches itself to a program or file so it can spread from one computer to
another, leaving infections as it travels. Much like human viruses, computer
viruses can range in severity: Some viruses cause only mildly annoying effects
while others can damage your
software or
files. Almost all
viruses are attached to an
executable file,
which means the virus may exist on your computer but it cannot infect your
computer unless you run or open the malicious program. It is important to note
that a virus cannot be spread without a human action, (such as running an
infected program) to keep it going. People continue the spread of a computer
virus, mostly unknowingly, by sharing infecting files or sending
e-mails with viruses
as attachments in the e-mail.

A worm is
similar to a virus by its design, and is considered to be a sub-class
of a virus. Worms spread from computer to computer, but unlike a virus,
it has the capability to travel without any help from a person. A worm
takes advantage of file or information transport features on your
system, which allows it to travel unaided. The biggest danger with a
worm is its capability to replicate itself on your system, so rather
than your computer sending out a single worm, it could send out
hundreds or thousands of copies of itself, creating a huge devastating
effect. One example would be for a worm to send a copy of itself to
everyone listed in your e-mail address book. Then, the worm replicates
and sends itself out to everyone listed in each of the receiver's
address book, and the manifest continues on down the line. Due to the
copying nature of a worm and its capability to travel across networks
the end result in most cases is that the worm consumes too much
system memory
bandwidth), causing Web
servers, network
servers and individual computers to stop responding. In more recent worm
attacks such as the much-talked-about .Blaster Worm., the worm has been designed
to tunnel into your system and allow malicious users to control your computer

Key Terms To
Understanding Computer Viruses:


A program or piece of code that is loaded onto your computer without
your knowledge and runs against your wishes.

Trojan Horse

A destructive program that masquerades as a benign application.
Unlike viruses, Trojan horses do not replicate themselves


A program or algorithm that replicates itself over a computer
network and usually performs malicious actions

blended threat

Blended threats combine the characteristics of viruses, worms,
Trojan Horses, and malicious code with server and Internet


antivirus program

A utility that searches a hard disk for viruses and removes any that
are found.

A Trojan
is full of as much trickery as the mythological Trojan Horse it
was named after. The Trojan Horse, at first glance will appear to be useful
software but will actually do damage once installed or run on your computer. Those on the receiving end of a Trojan
Horse are usually tricked into opening them because they appear to be receiving legitimate
software or files from a legitimate source. When a Trojan is activated on
your computer, the results can vary. Some Trojans are designed to be more
annoying than malicious (like changing your desktop, adding silly active desktop
icons) or they can cause serious damage by deleting files and destroying
information on your system. Trojans are also known to create a
backdoor on your
computer that gives malicious users access to your system, possibly allowing
confidential or personal information to be compromised.
Unlike viruses and worms, Trojans do not reproduce by infecting other files nor
do they self-replicate.

Added into the mix, we also have what is
called a blended threat. A blended threat is a
sophisticated attack that bundles some of the worst aspects of viruses,
worms, Trojan horses and malicious code into one threat. Blended threats
use server and Internet vulnerabilities to initiate, transmit and spread an
attack. This combination of method and techniques means blended threats can
spread quickly and cause widespread damage. Characteristics of blended
threats include: causes harm, propagates by multiple methods, attacks from
multiple points and exploits vulnerabilities.

To be considered a blended thread, the attack
would normally serve to transport multiple attacks in one payload. For
examplem it wouldn't just launch a DoS attack it would also install a
backdoor and damage a local system in one shot. Additionally, blended threats
are designed to use multiple modes of transport. For example, a worm may
travel through e-mail, but a single blended threat could use multiple routes
such as e-mail, IRC and file-sharing sharing networks. The actual attack
itself is also not limited to a specific act. For example, rather than a
specific attack on predetermined .exe files, a blended thread could modify
exe files, HTML files and registry keys at the same time basically it can
cause damage within several areas of your network at one time.

Blended threats are considered to be the
worst risk to security since the inception of viruses, as most blended threats
require no human intervention to propagate.

Combating Viruses, Worms and Trojan
The first steps to
protecting your computer are to ensure your
operating system
(OS) is up-to-date. This is essential if you are running a Microsoft Windows OS.
Secondly, you should have
anti-virus software
installed on your system and ensure you
download updates
frequently to ensure your software has the latest fixes for new viruses, worms,
and Trojan horses. Additionally, you want to make sure your anti-virus program
has the capability to scan e-mail and files as they are downloaded from the
Internet. This will help prevent malicious programs from even reaching your
computer. You should also install a
firewall as well.
A firewall is a system that prevents unauthorized
use and access to your computer. A firewall can be either hardware or software.
Hardware firewalls provide a strong degree of protection from most forms of
attack coming from the outside world and can be purchased as a
stand-alone product or in
Unfortunately, when battling viruses,
worms and Trojans, a hardware firewall may be less effective than a software
firewall, as it could possibly ignore embedded worms in out going e-mails and
see this as regular network traffic. For individual home users, the most popular firewall
choice is a software firewall. A good
software firewall will protect your computer from outside attempts to control or gain
access your computer, and usually provides additional protection against the most common
Trojan programs or e-mail
. The downside to software firewalls is that they will only
protect the computer they are installed on, not a network.
It is important to remember that on its own a
firewall is not going to rid you of your computer virus problems, but
when used in conjunction with regular operating system updates and a good anti-virus
scanning software, it will add some extra security and protection for your computer
or network.
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