This is the era of information technology. All matters are dealt digitally and communications are almost fully digitalized. Data and files including secret files are flowing from one end of world to other openly !! So to trouble a nation it is very easy now. Just disturb their communication line !!! The best method for this is putting computer viruses to the system through various methods.

Computer Viruses are simple  computer programs that spreads rapidly across computers by attaching a copy of itself to the files on your computer. When you run the infected files the virus get into action and began its destructive activities. When some one attach their removable devices like external HDD or pen drive it is transferred to them also.

Usually a Computer Virus is very harmful and can corrupt data , over write or modify files or use up many system resources and slow down the system. Some Computer Viruses  may be merely disturbing like asking to key in certain messages to continue or popping up some messages on the screen. Computer Viruses are usually written by expert programmers just to make trouble to others.

Computer Viruses of different types. They are broadly classifies into three as below.

1. Viruses that attack certain area or locations in computers. These viruses attack some specified locations only. The main among them are
   1. Boot Sector Virus that destroy the Master Boot Record ( MBR )
   2. File  Viruses that affect files
   3. Cluster Viruses
2. Viruses that attack computers in peculiar manner. They include
   1. Stealth Viruses
   2. Polymorphic Viruses
   3. Multi partite Viruses and
   4. Fast , slow and sparse infecting Viruses
3. Other types of Virus like disturbance are…
   1. Malwares
   2. Adware
   3. Spyware
   4. Spam
   5. Phising etc.

Many anti virus softwares are available in market to counter the Computer Viruses .