Rootkits are a malware inventor's dream: they are created to allow worms, bots, and other malevolent software to hide in plain sight. Rootkits are designed to hide themselves from detection by users and security programs, so they don't show up in Windows Explorer, the running processes don't display in the Task Manager, and many antivirus programs can't find rootkit-hidden malware.
A rootkit is a special program that buries itself deep into an operating system (like Microsoft Windows) for malicious activity and is extremely difficult to detect. The malicious software operates in a stealth fashion by hiding its files, processes and registry keys and it can be used to create a hidden directory or folder designed to keep it out of view from a user's operating system and security software.