What is a virus?
A computer virus
attaches itself to a program or file enabling it
to spread from one computer to another, leaving infections as it travels. Like
a human virus, a computer virus can range in severity: some may cause only
mildly annoying effects while others can damage your hardware, software or files. Almost all
viruses are attached to an executable file, which
means the virus may exist on your computer but it actually 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. Because a virus is spread by human action
people will unknowingly continue the spread of a computer virus by sharing
infecting files or sending emails with
viruses as attachments in the
email.
What is a worm?
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A worm is similar to a virus by 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 human action. A worm takes
advantage of file or information transport features on your system, which is
what 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 (or network bandwidth), causing Web servers, network servers and individual computers to stop responding. In 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 remotely.
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 (or network bandwidth), causing Web servers, network servers and individual computers to stop responding. In 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 remotely.
What is a trojan?
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.
