Computer virus is essentially a program worked out by some real talented man,incautiously or intended,who knows?Virus can replicate and spread in the computer system, from machines to machines through variouS media without any direct human intervention.Computer virus is likely to be attached to some executable programs or data files.Once these programs or files are executed,viruses become activated and duplicate themselves.They began to produce destruction,resulting in the loss or alteration of programs or data,more seriously leading to the collapse of the system.