A program or piece of code that is loaded onto your computer without your knowledge and runs against

your wishes. Viruses can also replicate themselves. All computer viruses are manmade.

A simple virus that can make a copy of itself over and over again is relatively easy to produce.

 Even such a simple virus is dangerous because it will quickly use all available memory and bring

the system to a halt. An even more dangerous type of virus is one capable of transmitting itself

across networks and bypassing security systems.

Since 1987, when a virus infected ARPANET, a large network used by the Defense Department and many

universities, many antivirus programs have become available.

These programs periodically check your computer system for the best-known types of viruses.

Some people distinguish between general viruses and worms.

A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other