Computer Virus

1. Definition:

A computer virus is a program that makes copies of itself and infects files. The technical definition of a computer virus is "a self-replicating piece of computer code that can partially or fully attach itself to files or applications, and can cause your computer to do something you don't want it to do".

Computer viruses can spread to other computers and files whenever infected files are exchanged and disrupt those computers' normal operations. Several thousand computer viruses are known, and on average three to five new strains are discovered every day.

Computer viruses got their name from biological viruses. Like a biological virus is small, cannot exist without a host, and can be passed from human to human, computer viruses are also small, cannot exist without a host, and can be passed from computer to computer or from program to program.

2. How viruses spread:

They certainly don't float around in the air like some human viruses. Instead, like any other computer program, a human must create them. Infections spread from machine to machine, and from organization to organization, in a number of ways.

In order to infect a computer, a virus has to have the chance to execute its code. Viruses usually ensure that this happens by behaving like a parasite, i.e. by modifying another item so that the virus code is executed when the legitimate item is run or opened.

As long as the virus is active on the computer, it can copy itself to other files or disks that are accessed.

Viruses can be transmitted by:

 Booting a PC from an infected medium.

 Executing an infected program.

 Opening an infected file.

Good vehicles for viruses include the parts of a disk which contain code executed whenever that disk is booted, and documents which contain macros executed whenever that document is opened with the relevant application.

The virus can't affect the computer's ROM (Read Only Memory), but it can affect RAM (Random Access Memory) and your computer disks. When your shut off your computer a virus that has been picked up will be lost, just like any other memory that is held in RAM. If the virus is on your disk or hard drive, it will return to the computer when you use the program again. If you switch from one program to another without shutting down the machine, the virus will attach itself to the new program. In this way, it can slowly infect all your programs before you know that it exists.

Common routes for virus infiltration include:

 Email attachments: Often infected files come as email attachments, even from people you know. The email senders have no idea that they are passing on a file with a virus in it. Today, most computer viruses are sent and received via email. Most require the user to open or run an attached document. However, some use system vulnerabilities to automatically run when downloaded. One of the most common places for a computer virus to appear is on a file found on the Internet or attached