This program does something undocumented which the programmer intended, but that the user would not approve of if he or she knew about it.
A.
What is a Virus.
B.
What is a Macro Virus.
C.
What is a Trojan Horse.
D.
What is a Worm.
Explanation:
A Trojan horse is different only in that the entire application was written to look like something else, when in fact it is an attack tool. An example of a Trojan horse is a software application that runs a simple game on the user’s workstation. While the user is occupied with the game, the Trojan horse mails a copy of itself to every user in the user’s address book. Then other users get the game and play it, thus spreading the Trojan horse.
Ref: Safe White papers; Page 70
SAFE: Extending the Security Blueprint to Small, Midsize, and Remote-User Networks