The definition of computer virus covers viruses, Trojan Horses, time bombs, and worms. The origins of computer viruses are explored, and several case studies are presented. Almost all viruses are planted in computer systems by hackers, agents of foreign governments, or disgruntled employees. Viruses are introduced directly into the targeted computer system or are caught through public domain software. Illegally obtained software and new software coming out of infected production sites are other common carriers. There are many virus detection and protection programs available; while this manual does not review specific programs, it does outline common characteristics. The author emphasizes that every organization must have a disaster recovery plan ready to implement when a computer virus infects the system. This book also discusses the computer underground and Bulletin Board Systems and profiles the typical computer hacker.