Computer viruses, worms, Trojan horses, and other exotic-sounding computer security have become a subject of considerable interest and concern in the computing and communications communities. This brief paper discusses the kinds of threats to security that such programs represent, and suggests some reasonable actions that computer and network users and owners can take to help minimize the risks. These threats are just beginning to be thoroughly studied, and this paper will by no means provide answers to all the problems they present. It is intended only to make the reader aware of the most essential definitions and issues, and to provide some references to further reading. © 1989.