Malware is harmful software. It is as old as the software itself. The programmers of malware have been trying to create them since they are trying hard to create legitimate software. There are multiple reasons why programmers create malware. These reasons may range from simple pranks to serious organized online crime. Among the so many types of malware, the most common types are viruses, worms, Trojans, spyware, and zombies. In this article, the inner working of most of the types will be stated in a very simple way.
Viruses :
The most well-known forms of malware are the virus which is akin to the biological 
counterparts because they are proficient of self-replication. What a virus does primarily, is not to cause damage but to clone itself against the other to spread further away. The damaged caused by a virus is easily detected, and so the creator employs furtive techniques to keep it unnoticed.
Sometimes damages are intentionally built by the creator. Some of the viruses are activated in certain times and silently spread for a few days or months or even years. They abruptly activate and perform its damaging function on a particular day. Still there are other viruses that are event driven and are activated when some particular event occur.
Worms:
The worms are very similar to a number of viruses, but key differences between them is worms are network-aware. The viruses reside in the files on the same computers. But, the worms don’t confine in one computer file, but can jump from computer to computer by seeking up-to-the-minute hosts in the network. Unlike viruses, the worms are capable of travelling world n a few seconds.
Trojans :
Trojans conceal inside the legitimate software. This malware replicates the story of Greek mythology that tells how the soldiers could 
able to enter into the fortified city by concealing them in a wooden horse gifted to the Trojan. At night the soldiers came out of the horse and hit the city. The disguises that the Trojans make are limited to the imagination of the programmer. The trick is to make the Trojans hidden in apparently risk-free game, pictures,videos, and even in genuine software package. In each case the cloaking is designed to entice it to run into the user’s own machine.
Spyware:
The spyware keeps observation on the user’s actions, and send out the gathered information to the hackers. It has no infection mechanism. Generally dropped by the Trojan or Viruses or Worms, it is automatically installed by itself on the user’s computer. It is so silent to be detected. After the installation, it starts collecting information like passwords, name, credit card numbers, email address. This way the malicious hackers can capture everything.
Zombies:
The infection mechanism of Zombies is same as spyware , though the scope is different. It, instead of collecting information from the 
computer, just sits there to receive commands from the hackers. The hackers can turn a huge number of computers to zombie machine, turning them under their disposal.
By now, it is clear to you about the malware and its result. Always keep guard your computer against the malware infection, otherwise, it might bring you irretrievable loss.