Virus, Trojan, Worm

Virus - an unwanted program or code that has entered and broken through the internet's security system from an action caused by the user. viruses usuallyt cause the user's computer to crash or run very slow.

Trojan - this is a hidden program or code which is found when downloading something you would think is safe into your computer. for example, downloading a song or free video game online. you would think its seirous and for fun but trojans may be hidden in the downloadable file.

Worm - this is very similar to a virus. it is an unwanted program that can cause damage but unlike a virus, which attaches itself to part of a program to become a virus, a worm does not need another program to work.