Which of the following statements would not be a proper definition for a Trojan Horse?

Which of the following statements would not be a proper definition for a Trojan Horse?

A.
An unauthorized program contained within a legitimate program. This unauthorized program performs functions unknown (and probably unwanted) by the user.

B.
A legitimate program that has been altered by the placement of unauthorized code within it; this code perform functions unknown (and probably unwanted) by the user.

C.
An authorized program that has been designed to capture keyboard keystrokes while the user remains unaware of such an activity being performed.

D.
Any program that appears to perform a desirable and necessary function but that (because of unauthorized code within it that is unknown to the user) performs functions unknown (and definitely unwanted) by the user.