What process involves the changing of a program's internal structure without changing the way the program works?

What is the item which could be matched with a statement below? software installed on a computer that produces pop-up ads using your browser an example of social engineering malware loads itself before the os boot is complete type of spyware that tracks your keystrokes, including passwords windows key + l the practice of tricking people into giving out private information or allowing unsafe programs into the network or computer when someone who is unauthorized follows the employee through a secured entrance to a room or building a type of malware that tricks you into opening it by substituting itself for a legitimate program a computer that has been hacked, and the hacker is using the computer to run repetitive software in the background without the user's knowledge an infestation designed to copy itself repeatedly to memory, on drive space, or on a network