i. Computer virus is a rogue software program that attaches itself to other software programs or data files in order to be executed and without user permission or knowledge. For example virus ILOVEYOU and CABIR.
ii. Worms are independent computer programs that can copy themselves from one computer to other computers over a network. They operate on their own without attaching to other computer program files and rely less on human behavior in order to spread from computer to computer. For example Sasser.ftp and MyDoom.A.
iii. Trojan horse is a software program that appears to be benign but then does something other than expected. The example of Trojan horse is Pushdo Trojan and Storm.