What is a trojan/worm/virus/logic bomb

23. What is a trojan/worm/virus/logic bomb?

This FAQ answer was written by Theora:

Trojan:
Remember the Trojan Horse? Bad guys hid inside it until they could get
into the city to do their evil deed. A trojan computer program is
similar. It is a program which does an unauthorized function, hidden
inside an authorized program. It does something other than what it
claims to do, usually something malicious (although not necessarily!),
and it is intended by the author to do whatever it does. If it's not
intentional, its called a 'bug' or, in some cases, a feature :) Some
virus scanning programs detect some trojans. Some virus scanning
programs don't detect any trojans. No virus scanners detect all
trojans.
Virus:
A virus is an independent program which reproduces itself. It may
attach to other programs, it may create copies of itself (as in
companion viruses). It may damage or corrupt data, change data, or
degrade the performance of your system by utilizing resources such as
memory or disk space. Some virus scanners detect some viruses. No
virus scanners detect all viruses. No virus scanner can protect
against "any and all viruses, known and unknown, now and forevermore".
Worm:
Made famous by Robert Morris, Jr. , worms are programs which reproduce
by copying themselves over and over, system to system, using up
resources and sometimes slowing down the systems. They are self
contained and use the networks to spread, in much the same way viruses
use files to spread. Some people say the solution to viruses and worms
is to just not have any files or networks. They are probably correct.
We would include computers.
Logic Bomb:
Code which will trigger a particular form of 'attack' when a
designated condition is met. For instance, a logic bomb could delete
all files on Dec. 5th. Unlike a virus, a logic bomb does not make
copies of itself.

Disclaimer:-i am not liable for any criminal or bad thing which you have done using this message and document. i am giving here for the educational purpose and care should be taken from your side before using this document and please get a written permission from the person before hacking or doing some thing in the network or system.This document is intended for judicial or educational purposes. I don't want to promote computer crime and I'm not responible of your actions in any way. If you want to hack a computer, do the decent thing and ask for permission first.please read and use this for useful purpose only to protect the systems and information from the bad people. always seek permission from the system owner or who ever responcible for the system by written and then go ahead. Give a full report with honestly to the person or company about your experiments and findings from the system. Always Do Good Think Good and Belive Good.