Why is a rootkit described as creating a back door into a system?

A rootkit is described as creating a back door into a system primarily because it allows an unauthorized user access to the operating system. This malicious software typically operates at a low level within the system, often gaining access to the kernel or other core components. Once installed, a rootkit can hide its presence while providing remote access to the system, enabling attackers to execute commands, steal information, or manipulate the system without being detected.

The other choices do not accurately reflect the nature of rootkits. While some might argue that security should involve controlled access, rootkits fundamentally undermine security by allowing unauthorized control. They do not ensure data is saved through hidden channels or automatically remove malware; rather, their main function is to conceal themselves and facilitate unauthorized access, which is the essence of what makes a rootkit dangerous.