Everything you wanted to know about Computer Viruses

What it all about About virus. History of virus. Types of virus. How virus spread. How it work. Protection from virus. Free to ask any question at any point

What is a virus? A virus is a computer program that enter a computer without permission or knowledge of the user and alter the way a computer operates. A virus is a software that piggybacks on other programs and change or delete the data, whenever those programs are run.

Why virus are called 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. Computer virus can self replicate themselves like biological virus. As biological virus, computer virus also effect the program or machinery in they exist.

History of virus Len Adelman coins the term virus in First virus “Elk Cloner” created by Rich Skrenta, in 1982 it attack Apple DOS 3.3 operating system and spread by floppy disk. In 1983, Fred Cohen writes a paper “Computer viruses – Theory and Experiments”

History of virus (continue) In 1986, two brothers Basit and Amjad Farooq Alvi created a boot sector virus called cBrain. Internet worms, in 1988 causes first Internet crises and shuts down many computers. Again in 1988, Jerusalem virus that activates on every 13 th Friday affects both.exe and.com files and delete any program that run on that day. In 2000, Denial of Service attack shuts down yahoo, Amazon and other web sites.

History of virus (continue) Love letter worm shuts down system in MY DOOM – the largest virus attack till date which effected one million computer world wide, was detected first on 26 January It affect one in every 10 message. Slow down internet performance by 10% and download time by 50%.

Types of virus File infector viruses Boot sector viruses Multi-partite viruses Macro viruses Script viruses Companion viruses

File Infector Viruses Attaches itself to other program files. When these programs are run from floppy, hard drive, or network they effect to other file. Many are memory resident. When any file that is executed in that memory also becomes infected. Examples: Jerusalem and cascade

Boot Sector Viruses Effect the system boot sector of a disk. (boot record on floppy/hard disks) Activate when user starts up from infected disk. Always memory resident in nature. Once in memory, all non-write protected floppy disks will become infected when accessed. Examples: Form, Disk Killer and Stoned

Multi-Partite Viruses Effect both boot records and program files. Difficult to repair. Boot area and files must both be cleaned from virus otherwise re-infection will occur. Examples: One_Half, Emperor, Anthrax.

Macro Viruses Most common type of virus. They are hard to detect. Effect program that contain macro programming language. Infect data files – word, excel, power point and access files. As these files are share more frequently they cause more damage.

Embedded with document. Therefore when edit from one file do not reflected in other files.

Script Viruses Effect various script languages such as DOS, Java Script, and Visual Basic Script.

Companion Viruses Execute through operating system rather than directly infecting programs or boot sectors. When you execute the command ‘ABC’, ABC.COM executes before ABC.EXE. Thus, a companion virus could place its code in a.COM file with its first name matching that of an existing EXE file. When the user next executed the ‘ABC’ command, the virus’ ABC.COM program would be run.

Other Threats to Computers Worm Torjan horse Trap door’s Bacteria

Worms Worms replicate themselves. Instead of spreading from file to file they spread from computer to computer, infecting an entire system. They steal user name and password and try to log in to other machine.

Torjan horse They look as a useful program but cause damage or do something malicious to a system. Don’t makes copies of themselves.

Trap Door’s It is secret point in a program that by passes standard authentication. Attackers leave behind trap door’s to reenter the system easily.

Bacteria They do not cause any destruction. They replicate themselves and thus consume system space.

How viruses spread By downloading infected files or programs from a network, there is a chance that you can encounter a computer virus. Once you RUN an infected program, the virus can spread rapidly, especially on networks. That is why the Internet, the largest network, is a fertile breeding ground for viruses. By inserting infected disks into your computer.

How viruses spread (continue)

How viruses spread (continued) Computers do get viruses from via internet. The virus will come in the form of some kind of attachment. Opening the attachment can give your computer a virus. Use of floppy disk, pen drives,etc.

Effect of virus Display a message

Effect of virus (continue) Erase vital data. Scramble data on a hard disk Cause erratic screen behavior Halt the PC Many viruses do nothing obvious at all except spread! Damage hardware

Effect of virus (continue) A denial-of-service attack is an attack that causes a loss of service to users such as loss of network connectivity. By consuming the bandwidth of the victim network.

How viruses works? Different virses uses different methods to operate. Like denial-of-service flood the incoming messages to the target system and thus consumes all bandwidth so forces it to shut down.

Working of File virus There are three basic techniques for infecting an executable file: Overwrite - An overwriting virus places itself at the beginning of the program, directly over the original program code. When you try to run this program, nothing happens except for the virus infecting another files.

Working of File virus (continue) Prepend – this virus put its code onto the file and when it is executed, virus code is first run then file gets executed.

Working of file virus (continue) Append -An appending virus places a “jump instruction” at the beginning of the program file, which moves the original beginning of the file to the end of the file, and places itself at that point, When you try to run this program, the “jump” calls the virus, and the virus runs.

Boot sector virus If CMOS is set up to boot from drive A: or from CD- ROM then the system boot sector (SBS) of the disk will be read. If the SBS contains a boot virus, the boot virus will become active, go inside memory It effect the system areas of the hard drive, and other disks that will access later on.

Protection from virus Install an anti-virus program. Regularly update your anti-virus. Examples - Norton Antivirus McAfee virus scan

Protection from virus (continue) Don’t open unknown files. Don’t use or share floppies, CD or pen drive without scanning with anti-virus. If you don’t know who the message is from, don’t open it. If you receive a suspicious message, delete it. Never double-click to open an attachment that contains an executable that arrives as an attachment.

Protection from virus (continue) Do not install pirated software, especially computer games. Regularly scan entire hard disk.

HAVE A NICE TIME