Trojan and Viruses

What is a trojan?
A trojan horse could be either:
a) Unauthorized instructions contained within a legitimate program. These instrcutions perform functions unknown to (and probably unwanted by) the user.
b) A legitimate program that has been altered by the placement of anauthorized instructions within it. These instructions perform functions unknown to (and
probably unwanted by) the user.
c) Any program that appears to perform a desirable and necessary function but that (because of unauthorized instructions within it) performs functions
unknown to (and probably unwanted by) the user.
…