Final answer:
Rootkits are software programs that can hide within an operating system and facilitate the installation of hidden files, granting unauthorized access and control to attackers while avoiding detection.
Step-by-step explanation:
Software programs that hide in the operating system and allow for the installation of hidden files are known as rootkits. These malicious tools can give attackers unauthorized access to a computer system without being detected by traditional security software. Not to be confused with Trojans which are disguised as legitimate software, worms that self-replicate to spread to other computers or spyware that secretly gathers user information, rootkits embed deep into the operating system and can intercept system calls, hide certain files, and provide administrative access to unauthorized users.