Different types of computer virus

A parasitic program written intentionally to enter a computer without the user's permission or knowledge. The word parasitic is used because a virus attaches to files or boot sectors and replicates itself, thus continuing to spread.
Many people are confused about different types of computer virus. The term computer virus is often used broadly to cover several types of malicious programs, including viruses, worms and Trojan horses. Each of them shares some similarities and some subtle differences.

- Computer Viruses : Computer viruses are parasitic programs that can replicate and spread to other computers. Computer virus needs a host program to run, so it often attaches itself to executable files. The virus codes run once you open the executive files. Computer viruses are spread by sharing infected files or email attachments.

- Computer worms : They can also replicate themselves, but unlike computer viruses, worms are self-contained. They can run and spread without being part of a host program. Worms spread at enormous speed in the network.

- Trojan horses : Trojan horses are hidden codes embedded within a legitimate program. Trojan horses are run without your knowledge, they can damage your files or create security leak in your system, allowing unauthorized users to access your computer. Unlike viruses and worms, they usually do not replicate themselves.