What is Computer Virus ?

Sep 18, 2020 · 3 min read
Image Credit: Google

A computer virus is a type of computer program which contains malicious executable statements that are self -reproducing in nature. It is a harmful activity which infects the host computer by deleting some files, acquisition of hard disk space or CPU time, stealing/corrupting personal data, target one path/file and corrupting it etc.

A computer virus was coined by Fred Cohen in 1984. But this name is given for its nature (self -replicating the program that infect the host computer or corrupt the software without user consent which is similar to biological virus).

Self -replicating means making an exact copy of itself by its own power.

History of Computer Virus

In 1949, John Von Neumann published a theory called “ Theory of self-reproducing automata” which tells how a computer program can be designed to reproduce itself. Due to this he is considered as the father of computer virology.

In 1972, Veith Risak published an article “ Self-reproducing automata with minimal information exchange” which describes the fully functional virus in assembler language for a SIEMENS 4004/35 computer system.

In 1980, Jürgen Kraus wrote a thesis “ Self- reproduction of programs” at the University of Dortmund and this thesis postulated that computer program behaves like biological viruses.

In 1981, Richard Skrenta, a ninth grader at Mount Lebanon High School wrote a computer virus that attached itself to Apple DOS 3.3 OS and spreads via floppy disk. On its 50th use the virus gets activated, infecting the personal computer and displaying “Elk Cloner: The program with a personality.”

In 1984, Fred Cohen wrote “ Computer Viruses- Theory and Experiments” which was the first paper to call self-reproducing program as a virus and this term introduced by his mentor called Leonard Adleman.

Leonard Adlemanone of the creator of the RSA encryption algorithm, for which he received the 2002 Turing Award (called the Nobel prize in Computer science).

Known Computer Virus : (Some only listed)

In 1987, Jerusalem virus. This virus executed on DOS which uses 2 kb of memory and infected executable files. On Friday 13,this virus deleted all executed files.

In 1999, Melissa virus released by David L. Smith. This virus targets Microsoft Word and Outlook which infects through E-mail. Sending mass mail by itself to the first 50 people in the user’s contact list and then disable multiple safeguard features on Microsoft Word and Microsoft Outlook.

In 2003, SQL Slammer. This virus attacked Microsoft SQL Server by buffer overflow (overruns the buffer’s boundary and overwrites the adjacent memory location). It generates random IP addresses to infect others. It spread rapidly, infecting most of its 75,000 victims within ten minutes.

Virus code snippets for fun (EDUCATION BASED ONLY)

Make A Virus To Open Notepad Repeatedly

@ECHO off


START %SystemRoot%\system32\notepad.exe

GOTO top

Virus To Make Multiple Folders

@echo off


md folder1

md folder2

md folder3

start folder1

start folder2

start folder3

goto RON

Checklists to avoid virus attack:

Update your system software to patch critical security holes and removing outdated features.

Avoid public network connection for internet.

Think before opening any attachments or downloadable file.

Enable firewall and anti-virus before entering into the internet.

If i’m a person who

Think before you Click. Happy Learning!


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