Nearly every computer user is susceptible to the 1st type of computer security risk- a computer virus, worm and/or Trojan horse.

A computer virus is potential damaging computer program that infects a computer and negatively affects the way that the computer works and without the users knowledge or permission. Once the virus infects the computer, it can spread throughout and may damage files and system software, including the system software. A worm copies itself repeatedly, for example in memory or on a network, using up resources and possibly shutting down the computer or network. A Trojan horse (named after the Greek myth) hides within or looks like a legitimate program. A certain condition or action usually triggers the Trojan horse. Unlike a virus or worm, a Trojan horse does not replicate itself to other computers.

Computer viruses, worms, and Trojans horses are classified as malicious-logic programs, which are programs that act without a user,s knowledge and deliberately alter the computer,s operations. Although these programs often are one of the three type (virus, worm, Trojan horse), some have characteristics of two or all three types. Melissa, for example is a virus, worm, and Trojan horse.

Unscrupulous programmers write malicious-logic programs and then test the programs to ensure they can deliver their payload. The payload is the destructive event or prank the program is intended to deliver. A computer infected by a virus, worm, or Trojan horse payload often has one or more of the following symptoms:

Screen displays unusual message or image; Music or unusual sound plays randomly; Available memory is less then expected; Existing programs and files disappear; Files become corrupted; Programs or files do not work properly;

Unknown programs or files mysteriously appear; System properties change;

Computer viruses, worms, and Trojan horses deliver their payload on a computer in three basic ways: When a user...