What is a Virus?
Sadhan
A virus is a manmade program or piece of code that causes an
unexpected, usually negative, event. Viruses are often disguised games
or images with clever marketing titles such as "Me, nude."
-----------------------------------------------------------------------------------------------------------------------------------------
What is a Worm?
Computer Worms are viruses that reside in the active memory of a
computer and duplicate themselves. They may send copies of themselves
to other computers, such as through email or Internet Relay Chat
(IRC).
------------------------------------------------------------------------------------------------------------------------------------------
What is a Trojan Horse?
A Trojan horse program is a malicious program that pretends to be a
benign application; a Trojan horse program purposefully does something
the user does not expect. Trojans are not viruses since they do not
replicate, but Trojan horse programs can be just as destructive.
------------------------------------------------------------------------------------------------------------------------------------------
Many people use the term to refer only to non-replicating malicious
programs, thus making a distinction between Trojans and viruses.