A virus is a program that can "infect" programs by modifying them to include a possibly evolved, copy of itself. A computer can become infected by files downloaded over a network, or by the installation of new software or floppy disks that are infected with viruses. Some viruses are only pranks, and perform harmless actions like displaying a screen with a joke message on it. Others can destroy files or wipe out a hard drive. Learn more about protecting your computer…