How A Computer Virus Works - Computer Sciences Textbooks

How A Computer Virus Works
By Glen F

A virus is a small computer program designed to do mischief by destroying data, altering information or even sabotaging entire computer networks.

The computer virus was originally a concept of science fiction. It was used in David Gerrold's book When Harlie Was Once in 1972 and also in John Brunner's The Shockwave Rider in 1975.

The concept in John Brunner's science fiction novel was a worm, the computing equivalent of a parasitic tapeworm, generating new segments for itself in all machines of a network and therefore unstoppable. Although this type of program was beyond the capability of programmers at the time.

The figurative use of the word virus is based on the biological virus which multiples itself within an organism. So too a computer virus has the same ability to replicate itself in a computers system.

A virus spreads by burying itself deep within the computer's disk operating system (DOS). The DOS is a set of instructions coordinating the activities of the disk drive, the keyboard, the monitor and the CPU that performs the arithmetic and logic operations. The DOS must run every time the computer is turned on.

Viruses tend to sneak past many users of computers because the viruses, like legitimate programs, are written in a computer programming language, a type of code made up of letters, numbers and other keyboard. A programming code gives instructions to the computer "behind the screen" so that most users are never aware that their system has been breached. Until it is too late.

As well as infected legitimate software or the illegal copying of software sold on disks, viruses are transmitted through the internet.

Once a virus has been discovered it is easy to write a simple program to delete the virus. Creators of such viruses, however, can just as easily upgrade their viruses to override such a program. Furthermore, some viruses can change the characters in their code every time they reproduce, making it almost impossible to stop them.

The first real virus was the subject of a computer science experiment in November 1983, presented by Fred Cohen, a professor of computer science at the University of Cincinnati in Ohio, to a seminar on computer security. He developed the first computer virus as part of his research on computer security for his doctoral thesis.

When Cohen introduced the concept to the seminar, the name virus was apparently suggested by Len Adleman.

According to Cohen, computer viruses are so easy to write that "anybody can do it". He said that it was possible in some programming languages to write a virus in as few as 11 characters.

By the second half of the eighties the virus had become a serious and prolific hazard to individual and corporate computer users; because the code copies itself into the computer's memory and then causes havoc, it became advisable to avoid using floppy discs which might conceivably contain a virus - freeware and discs supplied by clubs, for example.

In one famous incident, London's Royal National Institute for the Blind temporarily lost six months' worth of research after being attacked by a virus contained in files on a floppy disc. Considerable financial loss was suffered as a result of the epidemic, not to mention research time and valuable data.

The proliferation of viruses has seen the rise of a new business within the computer industry, the anti-virus. A number of software companies began to offer virus detection programs and 'good' viruses which could guard against threats.

Prevention is better than a cure: The best Antivirus Software available online free review

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