Computer viruses are programs that damage or disrupt normal computer functions. They attach themselves to files and replicate, spreading infection. Viruses can be transmitted via email, downloads, disks, and networks. Different types of malware include viruses, worms, Trojan horses, and hoaxes. To protect against viruses, users should install antivirus software, regularly update definitions and scan for viruses, avoid opening suspicious email attachments, and use firewalls.

1. Computer Viruses

2. What is a virus?
• A computer virus is a program that is
designed to damage or disrupt the
normal functions of your computer and
its files.
• Like biological viruses, computer viruses
attach themselves to a host, usually a
program file, data file, or a file in your
computer's operating system. From
here, it replicates itself, spreading the
infection to other files.

3. How viruses are transmitted from
computer to computer
• Viruses can find their way onto your
computer in many different ways.
• Viruses can be transmitted by email, in
downloads from the internet, through
network connections, by floppy disks or
by CDs, particular those that have been
burnt on a computer infected by
viruses.

4. What is a program
• A program is a recipe for a computer’s
behavior. Now, computers do not read
these things as we humans do.
• They cannot understand free text
messages – instead they have to rely on
numbers, because computers are really
only glorified calculators.

5. • For example, If the number 144 is
translated into binary it can be written
as 10010000 – which physically means
voltage on, off, off, on, off, off, off, off
in wires going into the processor.

6. • Computer viruses can cause very
serious damage to your computer's
program and data files, as well as affect
your computers hardware, such as your
hard drive. What a particular virus will
do to your computer depends on how it
was programmed when created.

7. MALWARE
• Viruses, Worms, Trojan horses, Logic Bombs
etc. are all examples of what is called
malicious software programs, or malware for
short.
• Malware is primarily an unwanted, uninvited,
potentially dangerous set of programs, but
there are important distinctions among the
different subtypes. The following overview
defines a few of the most important
categories:

8. VIRUS
• Viruses require a host, and their goal is to
infect other files so that the virus can “live”
longer. Some viruses perform destructive
actions although this is not necessarily the
case.
• Many viruses attempt to hide from being
discovered.
• Replicates?
• Yes. All viruses make copies of themselves,
infecting boot sectors, programs, or “data
files” as the opportunity arises.

9. WORM
• Worm viruses are self-contained programs
that remain hidden and propagate via email
or duplication, modify existing software so
that when run, the legitimate program
spawns copies of the virus, which is then
forwarded on in email or other files.
• Replicates?
• Yes. A worm makes copies of itself as it finds
the opportunity.

10. Trojan horse
• Trojan viruses pretend to be other software,
hence their name as in the Trojan Horse.
• Trojan viruses pretend to be a legitimate
piece of software, but in reality can attack
your hard drives, deleting files and re-writing
system files, causing your computer to
become unstable, particular when operating
system files are deleted.
• Replicates?
• No.

11. BOOT VIRUS
• Boot viruses attack the boot sectors on
your hard drive and interfere with your
computer's basic operation, making
your operating system run strangely or
even corrupt it all together.

12. • Boot viruses infect System Boot Sectors (SBS)
and Master Boot Sectors (MBS).
• The MBS is located on all physical hard
drives. It contains, among other data,
information about the partition table
(information about how a physical disk is
divided into logical disks), and a short
program that can interpret the partition
information to find out where the SBS is
located. The MBS is operating system
independent. The SBS contains, among other
data, a program whose purpose is to find and
run an operating system.

13. MACRO VIRUS
• Macro viruses tend to attack data files, like
word documents and spreadsheets, causing
you to loose files or cause your word or excel
software to not work properly.
• Ex. Microsoft Word files can contain
instructions that tells Word how to show a
particular document, Code Red is a binary
stream worm that employs the network.
Macro viruses are among the most common
viruses today. These are able to infect over
networks.

14. • As a general rule, computer viruses only
attack files in your computer. They do not
attack your computer's hardware, like the
monitor, mouse or keyboard.
• However, some viruses will attack the files
that operate your computer's hardware,
causing hard drives to reformat, video drivers
to be deleted or your operating system to
stop running.
• While this may cause your monitor to stop
working properly, it doesn't mean you need to
get a new monitor.

15. E-MAIL VIRUSES
• Email is probably the most common method
for spreading viruses. Plain text email
messages don't normally spread viruses. Most
email viruses are spread via attachments to
email messages, or in email messages
containing embedded executable code.
• For a virus contained in an email message to
attack your computer, it will normally require
your computer to executive some code, like
open an attachment or open a html link
embedded in the message.

16. E-MAIL VIRUSES
• To protect yourself against email viruses
it is important that you do not open
attachments from senders you don't
know, or come from a free email
source, like hotmail or yahoo.
• If you use an email client to check your
email, avoid clients that automatically
open attachments (like Outlook
Express).

17. Hoax
• A hoax is a chain letter, typically sent over e-
mail, which carries false warnings about
viruses or Trojans. This causes well meaning
users to send the warning on in the belief
that they are doing other users a favor.
• Often such warnings apparently sent from
well-known companies and organizations, but
this is not the case. Hoaxes may also contain
other messages that are supposed to trick
people to send the message on, for example
they will offer money or a cell phone as a
reward for forwarding the message to friends.

18. HOAX
• If you receive a warning about a virus, do not
pass the warning on to other users!
• This rule applies even if the virus actually
does exist, and applies doubly if the warning
asks to be sent on.
• Replicates?
• No, not by itself. They trick the user into
making copies instead.

19. Steps on how to minimize your
computer exposure to viruses
• The best way to minimize your chances
of getting a virus infection is to be pro
active and follow some basic steps
outlined below.
• Purchase and Install anti-virus software.
• Make sure the software you select is
compatible with your computer's
operating system, and offers an update
service.

20. • • Make sure that you regularly up date
your anti virus software definitions. New
viruses come out every day;
• so its important you make sure you
have updated your virus definitions.
Anti-virus software that hasn't been
updated for several months is practically
useless in protecting your computer.

21. • Make sure that you regularly scan your
computer for viruses using your anti-
virus software.
• If your software allows, use its
automatic protection features which will
check for viruses when ever you turn on
your computer.
• Virus scan any new programs or other
files that may contain executable files
before you run or open them,
particularly if it's a freeware or
shareware program.

22. • Scan floppy disks & CD’S before
opening them.
• • Don't open emails or email
attachments that have been sent by a
person or organization you don't know.
• Try to use an email client for checking
your email which doesn't automatically
execute or opens attachment.
• When you are browsing internet use
Fire wall.

23. Antivirus software's
• NORTON (SYMANTEC)
• AVG
• BIT DEFFENDER
• ANTIVIR
• McAFFE

24. FIREWALL
• SYGATE
• ZONE ALARM
• SYMANTEC NORTON
• MacAfee
• LAVASOFT