Everybody is scared of computer ‘virus’ as it does harmful actions on our computer. But when we look into the virus programming, we may certainly come out with the conclusion that it requires intelligence to code a virus. Virus program don’t have any specific rules. But it’s a common practice to include ‘signatures’ by virus creators. The main idea is to force the innocent user to run the programs. So certain viruses come along with so called ‘programmer utilities’ or ‘free tools’. Another thing is, it is easy to hang-up a working system using some ‘bad’ interrupts!