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. 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 programs. Then, the infected copy of the document containing a list of pornographic web sites would be attached to the email message. After that, the message would be sent to the first 50 contacts of each address book the virus encountered, and the process would repeat itself when the unwitting recipients opened the infected message. Corp. All Rights Reserved.