A computer virus a harmful file that could infect a PC's files and
the PC itself. There are many ways a virus can come to infect your
computer or laptop. Also, you can't see the file because they are
hidden within emails, downloads, and the Internet.
They can be sent by e-mails or downloads and can enter your drive
without your permission. Viruses, such as a worm, are able to attach
to a file, such as an email, and automatically send itself to
everyone in your address book. Anytime there is an email from an
unknown sender, avoid opening it and delete it. 
Most of these viruses
attach to main program files (.exe) because they are often used. (http://www.webopedia.com/DidYouKnow/Internet/2004/virus.asp) So
when you launch an infected executable file, the virus would become a
threat to many PC's. (These files can only move itself
if you are running program it's attached to.) Very quickly, the
virus will copy itself over and over. Viruses are very harmful and
can be anywhere on your computer without any of your knowledge.
A
type of virus a Trojan Horse. They don't replicate themselves.
Although, Trojans can destroy or erase some parts of your hard drive. (http://www.howstuffworks.com/virus.htm) These viruses are usually hidden inside files that
don't look dangerous. After you download the file, the hidden virus
will be onto your computer and go around in your files. If you were
to explore your computer folders, you won't see the virus. The only
way to get rid of the virus is an up-to-date anti-virus remover
program. The program can scan all of your files and folders and
remove it after a scan. It can also block harmful files from your PC.
A Trojan is a terrible virus that you can catch so you should be
careful on the Internet.
There is another virus
that
is also as harmful. A resident virus can be a threat to the files you
are running. It can multi-task so the 
virus can do more damage to
many files. Resident virus can harm, delete, or change files that
are running, saved, or just copied. This virus hides on your RAM. (http://www.e-learning-computing.com/is01cg/page_13.htm) They are tricky because resident virus stay in memory (therefore they
are named resident viruses).
The resident virus can do different things at once and are hidden
well.
If you were wondering where
viruses were come from, I can answer. One place would be that they
come from vandals/arsonists. Some people enjoy seeing things crash
and explode. If these vandals are smart in technical stuff, they
create evil viruses. For their own thrill, they create viruses and
send them through the web. Those viruses would soon blow up by being
the computer's threat. Also, there are arsonists who make these
programs to show off their abilities. They'd create a virus and send
it out (as many as they can or as destructive as they get) for some
sort of 'contest'. Or they'd just do it to brag to
others that they
know how to make a computer virus. Viruses can come from spies.
Those spies would want to steal a certain PC's password and a
virus could
find it. Spies also could use viruses to crash a PC for their own
persona
l reasons. Viruses come from sneaky spies or people who find
joy in destructive things. (http://computer.howstuffworks.com/virus1.htm) Viruses are mostly bad.
Although viruses damage the hard drive of your PC, there are some
“good” viruses. There are viruses that block your Internet 'hole'
from being a target of viruses. A virus that seemed good turned out
to be not so good. It was a virus that clears the Internet line so
that it is an easy opening for a virus to enter. Not all viruses are
bad but the “good” viruses can't always be trusted either. (http://computer.howstuffworks.com/virus6.htm)
In the web, viruses wander
around looking for victims. You should be careful on what you click
on. Opening an unknown email or image can send you a terrible virus.
The world is filled with villainous people who make programs to
destroy computers. Viruses are dangers so be cautious with the many
files on the Internet.
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