Which one of the following threats is used to facilitate the designer of a program or system which might leave a hole in the software that only he/she is capable of using?

The correct option is 2

Concept:

A trap door is a type of security threat in computer systems where a designer or programmer intentionally adds hidden entry points to the software, which can be exploited later for unauthorized access. These backdoors can serve as a secret method of bypassing normal authentication processes, enabling the person who knows about it (usually the one who created or installed it) to access the system or application without being detected.

Now a brief about the other options:

1. Spyware is software that collects information about users without their knowledge or consent.
2. A Trojan horse is a malicious program that is disguised as or embedded within legitimate software. Its purpose is to trick the user into installing it to cause damage, steal sensitive information, or gain unauthorized access.
3. A logic bomb is a type of malicious software that is triggered by a specific event or condition (such as a certain date/time or the presence of a specific file), upon which it performs some malicious activity.