A computer virus is a small software program created by hackers to spread from computer to computer and destroy or steal a computer's information, similar to how burglars steal property. There are several types of viruses like macro, email, Trojan, and worm viruses that can corrupt and delete files and spread to other computers via email to delete information on hard drives. Users can avoid viruses by keeping their computers protected with virus scanning software like MacAfee, Norton, or Windows Defender.