A rootkit is a program (or combination of several programs) designed to take fundamental control (in Unix terms "root" access, in Windows terms ...
http://en.wikipedia.org/wiki/Rootkit
Rootkit
A program for hacking root.
http://www.rootkit.com
RootkitRevealer
Scan your system for rootkit-based malware. ... RootkitRevealer is an advanced rootkit detection utility. It runs on Windows NT 4 and higher and its output ...