Difference between Virus ,worm and trojans

The most common Misassmption in computer terminology is wether to call a trojan virus or worm.
what is virus,what is a worm.While the words Trojan, worm and virus are often used interchangeably, they are not exactly the same.viruses worms trojans all are malicious programs which adversely effects the behaviour of computer.
What is a virus?
A virus is a computer program that alters the way the computer operates.A virus is a program that replicates itself on computer systems, usually through executable software, and causes damage.
 A virus can spread from one computer to other computer by opening a virus infected email atachment,clicking on a malicious link,transfering files from one to other.It will often place its self in executable paths there by decreasing cpu efficency.
What is a Worm?
A computer worm is a self-replicating malware computer program. The uncontrolable replication consumes sytem resources slowing or in some cases even aborting other tasks.
It uses a computer network to send copies of itself to other.It uses network flaws to spread.
This is in contrast to viruses, which requires the spreading of an infected host file. Although worms generally exist inside of other files, often Word or Excel documents, there is a difference between how worms and viruses use the host file. Usually the worm will release a document that already has the "worm" macro inside the document. The entire document will travel from computer to computer, so the entire document should be considered the worm.
Ex:prettypark.worm
What is a trojan Horse?

Trojan is a malware that may appear to be legitimate but infact it does malicious activities .It access the users Remote information.Unlike viruses it doenst replicate causing the system to work slow(reducing the processing power,cpu utilization) but they can make a hell of job .Trojan alters the behaviour of computer by uncontrolable popups,adware
These trojan horses are used by hackers to steal the personal information.