What is a Computer Virus?
A computer virus is a computer program that
can copy itself and infect a computer without the
permission or knowledge of the owner.
One of the first detected virus was the Creeper
virus in the early 70’s
Before computer networks became widespread,
most viruses spread on removable media,
particularly floppy disk.
Basic Computer Viruses
appears as interesting program file but when installed
it allows intruders to access and read your files
virus that copies and multiplies itself by
using computer networks and security
use e-mail messages to spread which allow it to
automatically forward itself to thousands of people
Types of Viruses
Boot Sector Virus
Infects the boot or MBR of diskettes and hard drives through the
sharing of infected disks and pirated software applications
Once your hard drive is infected all diskettes that you use in your
computer will be infected
Becomes active when the program file (usually with
extensions .BIN, .COM, .EXE, .OVL, .DRV) carrying the virus is
It then makes copies of itself and will infect other programs on
Hybrid of a Boot Sector and Program viruses
It infects program files and when the infected program is active it
will affect the boot record
Types of Viruses
Disguises itself to prevent from being detected by antivirus
It alters its file size or conceals itself in memory
Act like a chameleon, changing its virus signature (binary
pattern) every time it multiples and infects a new file
Programmed as a macro embedded in a document, usually
found in Microsoft Word and Excel
Once it gets in to your computer, every document you produce
will become infected
Relatively new type of virus and may slip by your antivirus
software if you don't have the most recent version installed
Signs Your Computer is Infected
Functions slower than
Responds slowly and
Restarts itself often
See uncommon error
menus, and dialog boxes
Notice applications fail to
Fail to print correctly
First half of the 70'Late 60,s, early 70,s- "Rabbits" cloned
themselves occupied system resources, slowing down the productivity.
-"The Creeper" capable of entering a network by itself and transferring a
copy of itself to the system.
Early 80,s-Increasing number of programs written by individuals not by
software companies. Programs caused miner viruses called "Trojan horses".
1986'Brain virus' - by Amjad and Basit Farooq Alvi.
spread through floppy disks,
infected boot records and not computer hard drives
Lahore, Pakistani Brain, Brain-A and UIUC virus
-took over free space on the floppy disk and hid from detection
”disguised itself by displaying
the uninfected boot sector on the disk.”
- the first memory resident file infector that attacked executable files and
took control when a file was opened
The Jerusalem Virus
-had bugs that re-infected programs that were already infected
1988: Robert Morris made a worm that invaded ARPANET computers
- disabled 6,000 computers on the network by overflowing their memory banks
with copies of itself
1991: Norton Anti-Virus software
1999: "Melissa" virus
-infected thousands of computers very fast by sending copies of itself to 50
names in the address book on Outlook e-mail
- Led to an estimated $80 million in damage and record sales of anti-virus
2000: "I Love You" virus
-was sent by email and infected 10 % of computers in only one day
-created by a young Filipino computer student who did not get punished
because then the Philippines had no laws against hacking which led to the
European Union's global Cybercrime Treaty.
2001: "Nimda" virus (days after 9/11)
-had 5 ways of infecting systems
MyDoom spreads through emails and file-sharing software faster
than any previous virus or worm.
Allows hackers to access the hard drive of the infected computer.
An estimated one million computers running Windows are
affected by the fast-spreading Sasser computer worm.
The worm does not cause irreparable harm to computers or data,
but it does slow computers and cause some to quit or reboot without
Discovery of the first-ever malware trojan horse for Mac OS X
Torpig is a Trojan horse which affects Windows, turning off antivirus applications.
It allows others to access the computer, modifies data, steals
confidential information and installs malware on the victim's
Conficker infects anywhere from 9 to 15 million Microsoft server
French air force, Royal Navy warships and submarines,
Sheffield Hospital network, UK Ministry of Defence, German
Bundeswehr and Norwegian Police were all affected.
Total Number of Viruses by year
January 1985 1
January 1987 3
January 1989 6
January 1990 142
January 1991 357
January 1992 1,161
January 1993 2,482
January 1994 3,687
January 1995 5,626
January 1996 7,764
January 1997 11,037
January 1998 16,726
January 1999 40,850
January 2000 44,000
January 2001 48,000
January 2002 55,000
January 2003 62,000
Another virus that fired up the media was Melissa, a Word macro
When people received the host Word document via email and
opened it, the virus sent a copy of itself to the first 50 people in the
victim's address book.
Named after a topless dancer in Florida, the Melissa virus crashed
the email servers of corporations and governments in different
spots around the world.
The Computer Emergency Response Team, set up after Robert
Morris mucked up the Internet with his worm in 1988, estimated that
the virus hit 100,000 computers in its first weekend.
David L. Smith posted the infected file to an alt.sex usenet group
using a stolen AOL account. Initially he entered a plea of
innocence, but after being confronted with a maximum sentence of
40 years in prison, he eventually pled guilty and received a muchreduced sentence.
Love You, Love Bug
By almost any measure, the so-called Love Bug was the most
damaging and costly virus ever. I don't know who comes up
with these whack figures, but according to Reuters the bug
cost the world $15 billion in lost productivity.
The Love Bug spread far faster than Melissa. Unlike Melissa,
it would mail itself to everyone in your Outlook address book
-- most of whom would probably be delighted to read about
how you love them -- not just the first fifty. Moreover, it would
gobble up certain media files stored on your hard drive.
Did you know?
One German newspaper
tragically lost 2,000
pictures from its archive.
The perpetrator turned out
to be a 23-year-old Filipino
computer science student
who more or less
plagiarized all of his code.
The lack of laws in the
computer crimes, he pretty
much got away with his
Upload and use antivirus
Be aware of the e-mails
and attachments you
Check for updates on
Make sure antivirus
software is installed