Final answer:
A rootkit allows a hacker to gain nearly complete control of a computer without the owner's knowledge. It hides itself from the system and can modify operating system calls to remain undetected. This provides the attacker with administrative-level access quietly.
Step-by-step explanation:
A rootkit allows a hacker to gain access to your computer and take almost complete control of it without your knowledge. Unlike a denial of service (DoS), which overwhelms a system with traffic preventing legitimate access, or a logic bomb, which triggers malicious activity when certain conditions are met, a rootkit provides deep access to the system. Rootkits are designed to be hidden to the user and can intercept and alter operating system calls to conceal their presence, often giving the attacker persistent administrative-level access to the system.
Hackers use various methods to compromise systems, such as persuading people to click on links or disclose personal information. A system compromised by a rootkit may function normally, giving no indication to the user that their security has been breached. This stealth allows attackers to steal information, execute commands, or create backdoors for future access.