Disks inserted into an infected computer can pass the virus along to other computers. The rate of infection depends on how often disks are shared. Once detected, such viruses can be contained. A newer way to share files, the Internet, has allowed viruses to spread more rapidly than ever. The Internet links millions of computers together in a way that makes infection a strong possibility.
People create and unleash computer viruses for multiple reasons.
Some are taking revenge against a particular computer system, while others are playing practical jokes. Many are created to simply show off their designers' skills and wreak as much havoc as possible. The damage that a virus can have on your computer can range from a minor, annoying behavior to the deletion of everything on your computer's hard drive. Were a destructive virus to attack your computer, it would only cost you the time spent to restore your hard drive. Lost data and wasted time caused by viruses really adds up, though, when looked at globally.