Computer
Virus Basics
A computer
virus is created when a programmer creates computer code that
has the capability to replicate itself, hide, watch for a certain
event to occur, and/or deliver a destructive or prankish payload
on a disk or in a computer program. Viruses can attach themselves
to just about any type of file and are spread as infected files
are used by other computers. Some viruses are relatively harmless,
while others are very devastating. They can destroy files, software,
program applications, and cause the loss of data.
New computer
viruses are constantly being created by malicious programmers.
Because of this, it is vital to keep anti-virus software on computers
up-to-date. Some anti-virus software programs allow users to set
them to silently check for updates whenever users are connected
to the Internet. Others remind users to periodically check for
updates.
Worms and
Trojans are closely related to viruses. A worm makes copies of
itself on a computer, rather than infecting other files like viruses.
A Trojan is a program that secretly installs itself on a computer
and opens a back door to the computer so that malicious attacks
can be remotely controlled. The actual Trojan is usually not damaging
at first, but it is usually accompanied by other damaging programs.
To protect
your home computer against computer viruses, worms, and trojans,
you should invest in anti-virus software, such as the software
offered by Norton or McAfee. You should also make sure it stays
up-to-date. Virus protection software on school computers is regularly
updated by the school system network technicians.
What Computer
Viruses Infect
Viruses can
enter computers in many ways. Once a virus has entered a system,
it will generally hide until it is unknowingly run by the user.
A virus will not act until it has been run or some pre-established
condition has been met, such as a specific date. The effects of
a virus may not be noticed for some time after it has infected
a computer.
Viruses can
infect several components of a computer's operating and file system
including:
- System
Sectors/Boot Records - Viruses can infect the parts of the
system that are used to run programs and perform functions such
as start up and shut down.
- Files
- Viruses can infect program files. These viruses stick to program
files such as .com, .exe, .sys, etc. Some viruses hide in the
memory of the computer at first, while others simply attack
a specific software program, such as Microsoft Word.
- Companion
Files - Viruses can create companion files that are a special
type of file that adds files that run on the hard disk.
- Macros
- Viruses can infect macro or data files.
- Disk
Clusters - Viruses can infect files through the disk directory.
- Batch
Files - Viruses can use batch files to infect a computer.
- Source
Code - Viruses can be in additional code that is added to
actual program source code.
- Visual
Basic Worms - These worms use the Visual Basic programming
language to control a computer and perform tasks.
Types of
Computer Viruses
Viruses are
categorized by how they infect computers. Some viruses fall into
more than one of these categories.
Types of viruses
include:
- Polymorphic
Viruses - Polymorphic viruses change characteristics as
they infect a computer.
- Stealth
Viruses - Stealth viruses actively try to hide themselves
from anti-virus and system software.
- Fast
and Slow Infectors - Fast and Slow viruses infect a computer
in a particular way to try to avoid being detected by anti-virus
software.
- Sparse
Infectors - Sparse Infectors don't infect very often.
- Armored
Viruses - Armored viruses are programmed to make eradication
difficult.
- Multipartite
Viruses - Multipartite Viruses are viruses that may fall
into more than one of these categories.
- Cavity
(Spacefiller) Viruses - Cavity (Spacefiller) viruses attempt
to maintain a constant file size when infecting a computer in
order to try to avoid detection.
- Tunneling
Viruses - Tunneling viruses try to "tunnel" under anti-virus
software while infecting.
- Camouflage
Viruses - Camouflage viruses attempt to appear as a benign
program.
- Virus
Droppers - Virus Droppers are a special category of programs
that place viruses on computers but are not by themselves an
actual virus.
Ways to
Catch a Computer Virus
There are
several ways to catch a computer virus:
- From
Floppy Disks - Be very careful about putting a floppy disk
that has been in another computer in your computer, even if
it is from a trusted source.
- From
the Internet - Viruses can be attached to various types
of Internet files, such as graphics and program files that people
download from the Internet. Just browsing the Internet does
not put your computer at risk. You have to download and install
a file for a virus to be able to infect a computer.
- From
E-Mail - Viruses often travel via e-mail attachments. E-mail
messages by themselves do not carry viruses. Only .exe, .com
or other types of executable files can carry a virus.
- From
a Computer Network - Computer Networks are groups of computers
linked together by a large computer called a server. The server
and these computers constantly share information. If one file
that is used by several network users becomes infected with
a virus, the virus will quickly spread to the other users.
Symptoms
of a Computer Virus
The following
are some possible indications that a computer has been infected
by a virus. These problems can also be caused by non-virus problems,
but they are the most reported symptoms of a computer virus infection.
- Computer
programs take longer to load than normal.
- The computer's
hard drive constantly runs out of free space.
- The floppy
disk drive or hard drive runs when you are not using it.
- New files
keep appearing on the system and you don't know where they came
from.
- Strange
sounds or beeping noises come from the computer or keyboard.
- Strange
graphics are displayed on your computer monitor.
- Files have
strange names you don't recognize.
- You are
unable to access the hard drive when booting from the floppy
drive.
- Program
sizes keep changing.
- Conventional
memory is less than it used to be and you can't explain it.
- Programs
act erratically.
If You
Get a Computer Virus
At school:
- If you
are on a school computer, contact your school tech leader or
submit a request to computer support, immediately.
At home:
- If you
do not have an anti-virus program, get one immediately. Many
anti-virus programs can be downloaded from the Internet.
- Install
the latest virus updates available for your anti-virus software.
(Generally, you can get these updates at the anti-virus program
web site.) Then run the anti-virus software to identify the
virus. Most software will ask users to choose whether to clean
the virus, delete the file, or ignore it when a virus is found.
- After getting
rid of a virus, run your anti-virus software again to make sure
the virus has been eradicated.
- Find an
Internet web site that contains descriptions of viruses and
search for information about the virus you have found on your
computer.
- If you
get an e-mail virus, contact everyone in your address book and
tell them to be on the lookout for suspicious e-mails and attachments.
Do not send any e-mails until you are sure the virus has been
cleaned from your computer.
Safe Computing
Practices
There are
several things you can do the help protect your computer against
viruses:
- Anti-Virus
Software - If you don't have an anti-virus software program,
invest in one.
- Scan
Your Computer on a Regular Basis - Scan you system with
anti-virus software regularly.
- Update
Your Anti-Virus Software on a Regular Basis - Keep your
anti-virus software up to date. Do this at least weekly and
more often if there are news reports of a new virus threat.
- Backup
- Backup your files on a regular basis. Always maintain copies
of files you can't do without, just in case your computer gets
infected and crashes.
- Turn
off E-Mail Preview - Turn off the preview function if your
e-mail software has one.
- Scan
Floppy Disks - Scan floppy disks from other computers with
anti-virus software before you use the disk. Simply place the
disk in your floppy drive and run the anti-virus software program.
If a virus is found, most programs will give you several choices
about what to do, such as removing the virus, doing nothing,
or deleting the file that contains the virus.
- Protect
Your Floppy Disks - Write-protect any floppy disk you place
into another computer. If the other computer has a boot sector
virus, the write-protect on the disk will prevent it from becoming
infected with the virus.
- Scan
Downloaded Files - Scan downloaded Internet files with anti-virus
software before you use or run them.
- Scan
All E-Mail Attachments - If you receive an attachment you
need to view, scan it with anti-virus software before you open
it.
- Beware
of E-Mail Attachments from Unknown Sources - If you receive
an unexpected attachment from an unknown source, delete it.
Never open attachments for files that end in .vbs (Visual Basic
Script) or .js (Java Script). Viruses often travel in these
types of files.
- Be Alert
- Pay attention to news about virus alerts. You might want to
subscribe to a virus alert e-mail notice from one of the anti-virus
software makers.
Desanto, M.
(1999). Computer virus tutorial. Retrieved April 15, 2002 from
http://shareware.about.com/library/weekly/aa022299.htm.
Shelly, G.B,
Cashman, T.J. & Vermatt, M. E. (2001). Discovering computers
2002: Concepts for a digital world. Boston, MA: Course Technology.
