Beware the worm, the virus, and the Trojan Horse. Despite advances in authentication and encryption methods, computer systems are just as vulnerable as ever. It is written at a level that can be understood by almost anyone who ever had to log into a computer system, and possibly by a congressman or corporate vice-president.
Many systems suffer a wide range of simple insecurities.
Throughout this article the word BUG is meant to bring to mind a concealed snooping device as in espionage, or a microorganism-carrying disease as in biology, not an inadvertent programming error. The simplest kind of Trojan horse turns a common program like a text editor into a security threat by implanting code in it that secretly reads or alters files in an unauthorized way. In other words, the program runs with the user's own privileges. The neat thing about this, from the point of view of whoever plants the bug, is that the infection can pass from programs written by one user to those written by another, gradually permeating the whole system. Once it has gained a foothold it can clean up the incriminating evidence that points to the originator, and continue to spread.