What is a Virus

A virus is a program that infects data or program of our computer. It gets activated by its host program. It replicates itself everytime the user runs the infected program.

How Virus Spreads ?

The most common way through which a virus spreads in through floppy transfer. When an infected floppy is loaded into the computer. It transfers the virus to hard disk. Then the virus there untill if is removed.

Types of Viruses

Parasitic VirusBoot Virus

1.Parasitic Virus – Parasitic Virus attaches itself to other programes and gets activated when host program is excuted it spreads to other computers when affected programes are copied.

2.Boot Virus- These virus affect the boot sector of the disk. It works with replacing the first sector on the disk with part of itself. It occupies master boot sector on hard disk.


1. C-Brain – This virus was developed by two Pakistani brothers. This virus stays in the boot sectors and gets activated after a random number of interupts are executed. It corrupts the file allocation table (FAT) making the data disc unreadable.

2. Cascade – This virus attached itself to IBM PC’s. The letters are seen droping vertically down to the bottom of the screen. It is a parasitic virus. This virus attached itself to COM and EXE files to damage the data.

3. Columbus or October the 13th Virus – This virus is programmed to attack on 13th October. This virus enters COM and EXE files and destroys hard disk and contents of disk are rendered unreadable.

4. PC Stoned or Marijuana – This virus resides in boot sector. It damages of the floppy of drive A and spreads to other computers. It damaged some sectors of FAT. Whenever the PC is booted the virus copies itself on to the boot sector of the disk thus corrupting the disk.

5. Ajani ST Virus – This virus copies itself onto every non-write protected disk used. When a certain limit in reached it writed random data across the central directory and FAT making the disk unusable. The virus then removes itself from the computer.


1. Jewsalem – Activates only on Friday

2. Maclon – Destroys hard disk and application software

3. Loreli Virus – Activates on 13 May and slows computer on 13 of May month

4. Lehigh Virus – Destroys data by writing zeros to the first 32 sectors of disk which erases the directory and makes data unrecoverable.

5. Die Hard Virus – This virus attacks the boot sector and formats the hard disk as we run the computer. This makes the disk unreadable. In some cases it damages the hard disk each time we switch. See virus actions.


Boot Parasitic and Boot Viruses work in their own way. The boot virus resides in the boot sector and corrupts the FAT thus making the disk unreadable. The Parasitic Virus attaches itself to the host program thereby destroying or corrupting the program data. It destroys whole of the application software that we run on your computer.


1. Never use floppy disk’s brought from outside directly on the your computer, first check the floppy for virus.

2. Keep all masterEXE and COM files in a write-protected disk.

3. Avoid playing Games where important data is stored, as virus spreads faster through games.

4. If a virus is found on a computer, isolate it, identify it and then remove the virus.

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