WHAT IS A "VIRUS"?
Computer viruses are called viruses because they share some
of the traits of biological viruses.
A computer virus passes from computer to computer like
a biological virus passes from person to person.

BIOLOGICAL VIRUSES
• A biological virus is not a living thing
• A virus is a fragment of DNA inside a protective jacket
• A biological virus must inject its DNA into a cell
COMPUTER VIRUSES
• A computer virus must piggyback on top of some other program
or document in order to get executed
• Once it is running, it is then able to infect other programs or documents
WHAT IS A "VIRUS"?

VIRUS HISTORY
Traditional computer viruses were first widely seen in the late 1980s
Viruses took advantage of these three facts to create the first self-
replicating programs!
FIRST FACTOR
Spread of personal computers
SECOND FACTOR
Use of computer "bulletin boards"
THIRD FACTOR
The floppy disk

1. FILE INFECTORS VIRUSES
a. Embedded in program
b. Runs when program gets executed
c. Loads in memory
d. Cycle continues through sharing files
2. BOOT-SECTOR VIRUSES
a. Load viruses into memory
b. Infect the boot sector on floppy disks and hard disks
3. MACRO VIRUSES
a. Infects data files
b. Executed in embedded scripts
c. Inserts copies of itself into other documents
d. Spreads by sharing data files
CLASSES OF VIRUSES

1. Large size of today's programs (executable)
2. Operating systems now protect the boot sector
EXECUTABLE AND BOOT SECTOR VIRUSES
ARE NOT VERY THREATENING ANY MORE
CLASSES OF VIRUSES

E-MAIL VIRUSES
E-MAIL VIRUSES ARE THE LATEST INVENTION
1. Melissa Virus (March 1999)
a. Embedded into Word document
b. When opened, sent to first 50 email addresses in address book
c. Included a friendly note making it look harmless
d. If opened by any of the recipients, sent to another 50
addresses of the current recipient
1. The ILOVEYOU Virus (May 2000)
a. Attachment is a piece of code
b. When executed, sent itself to everyone in the address book
c. Corrupted files

ORIGINS
THREE REASONS PEOPLE CREATE VIRUSES
1. The same psychology that drives vandals and arsonists
2. The thrill of watching things destroyed
3. Bragging rights, or the thrill of doing it

FIGHTING VIRUSES
ANTIVIRUS PROGRAMS
- Norton Antivirus (Symantec)
- VirusScan (McAfee)
- F-Secure Anti-Virus (F-Secure)
No anti-viruses guarantee 100 percent protection from viruses!!!

1 I-Worm.Klez 96.49%
2 Win95.CIH 0.84%
3 I-Worm.BadtransII 0.52%
4 I-Worm.Hybris 0.30%
5 Trojan.PSW.Delf 0.24%
6 I-Worm.Sircam 0.21%
7 Win32.Elkern.c 0.16%
8 Macro.Word.Cap 0.13%
9 Win32.FunLove 0.09%
10 I-Worm.Magistr 0.07%
Position Name Number of occurrences
STATISTICS

STATISTICS
NUMBER OF INFECTED FILES BY COUNTRY, WITHIN THE LAST 30 DAYS
0-100
101-1000
1001-10,000
10,001-100,000
100,001+